K League Coach: Evaluating Leading Scorers in K League

The K League Coach is back with more in depth analysis, this time taking a detailed look at the top scorers in K League 1 after Round 14. By looking at statistical data, the Coach highlights how players' goal scoring abilities compare to other leading marksmen in Korea's top division, and different statistical interpretations that can be used to gain more of an insight into their performances.

Introduction

This article will take a closer look at the leading goal scorers up to Round 14 in the 2019 K League season, only K League goals will be included; Asian Champions League and Korean FA Cup games will not be factored in. Looking at the opening 14 rounds of the season we will see how players' goal scoring performances compare to one another, and different statistical interpretations that can be used to gain more of an insight into their performances.

We will then use these insights to see what it may suggest regarding the players' output over the coming season and the different factors which coaches must consider when selecting the team or potential transfer targets. The relationship between leading scorers and team performance will also be discussed.

Part 1: Leading Goalscorers

After the opening 14 rounds of the 2019 K League 1 season those with four goals or more were selected for analysis; this gave us a group of 16 players to start with. 

These 16 players came from nine of the 12 K League 1 clubs. Incheon United, Seongnam  FC and Pohang Steelers were the three clubs not to have a player who scored four goals by this point in the season. These teams found themselves placed 12th, 9th and 6th respectively. 

Leading K league scorer after week 14 of the 2019 season

It is worth noting that Jeju United have two of the 16 players players despite sitting second bottom of the league. After 14 games Jeonbuk Hyundai Motors sit top of the table but only have one player to have scored four or more yet Jeonbuk as a team have scored more than double the amount of goals which Jeju United have. Ulsan Hyundai have three players in this selection and currently sit in second place.

Kim Shin-wook of Jeonbuk Hyundai (R) in action against Gyeongnam FC.

On first impressions, Kim Shin-wook and Aleksandar Pešić are currently the best marksmen in the league. Kim has performed to a high level in the K League for a sustained period of time whilst Pešić has recently joined FC Seoul with big expectations.

When looking at the performances of goalscorers it is important to discount goals scored from penalties. With such a high rate of return, penalties can distort the understanding of a player's performance. It may also lead to what appears to be a disparity in performance, simply because one player takes penalties for his team and another does not.

Leading K League 1 Goalscorers minus penalties after Round 14 of the 2019 Season

After deducting penalty kicks Kim Shin-wook becomes the outright leading goal scorer for this period. Three players now fall below the four goal point so Mango Cruz (Jeju United), Kim Bo-kyung (Ulsan Hyundai) and Yeom Ki-hun (Suwon Bluewings) are now removed from consideration. It is important to note that Kim Jin-hyeok will now take part in six-week basic military training before joining up with Sangju Sangmu as part of the player's mandatory military service.

Coaching Considerations

When evaluating goal scoring performance it is important to differentiate between goals from open play and penalties. For a more detailed understanding of how your team is performing, coaches may wish to look a goals from open play, goals from penalties, direct free-kicks or set pieces, to really see where the team is doing well or where it may need to improve. Simple goals-scored tables are of little use to understand performances levels and areas to coach in the future.

Part 2: Goals Excluding penalties vs Expected Goals

A closer examination is made of the remaining 13 players. Their goals, minus penalties, were compared with their individual expected goals. Expected goals (xG) is the number of goals a player would be expected to score from the shots which they take. The value of each shot is based upon several variables such as assist type, shot angle and distance from goal, whether it was a header and whether it was defined as a 'big chance' with few defenders in the way of goal. This data was provided by Wyscout.

Expected goals of K League 1 Leading scorers after Round 14, excluding penalties 

Eight of the remaining 13 players are currently outperforming their xG, and in the cases of Pešić, Park Yong-ji, Bae Ki-jong and Kim Jin-hyeok, significantly so. Tiago Marques and Cesinha are on track with the average expected rate of conversion for the chances they had. Edgar Silva is the player who is under performing compared to their xG the most, having only scored four goals compared to the seven which would have been scored from his chances on average.

The question moving forward for these high performing players is if they can maintain their current ability to convert at a better rate than expected. For players such as Edgar Silva, it is a question of if his current under performance is a temporary slump and he will soon be scoring more goals from the opportunities he is being given, or do they need to be replaced?

Plotting players on a graph using their goals scored, excluding penalty kicks, and their xG helps illustrate their performance relative to one another. Using the graph below, the better a player is performing the closer towards the bottom right corner they will be. Being placed here would mean they have a high goal scoring rate from more limited opportunities and have far outperformed the average expected rate of conversion.

Goals scored compared to xG of the leading scorers in K League 1 up to Round 14.

It is possible to quickly identify those converting at a lower rate than expected, those on par with the average, and those out performing their xG. Kim Shin-wook is currently in excellent form, not only outperforming his xG, but doing so from the fourth highest xG meaning he is getting good quality or a high number of chances to score. 

Daegu currently have three players who sit on four goals, but this graph clearly shows the difference in their performance level. Kim Jin-hyeok has had few opportunities to score and done incredibly well to convert four of them. Cesinha is almost perfectly following the statistical average conversion rate, while Edgar Silva should have scored more from the chances he has had. It is only this closer analysis that shows the difference in what may have been perceived as equally good form between the four players from the original leading scorers table.

For more context, below is the same format of graph with the leading scorers from the 2018 K League season. After deducting penalty kicks nine players reached double figures over the course of the 38-game season. Six of the top nine scorers were able to outperform their xG, though Ricardo Lopes of Jeonbuk Hyundai Motors only by the slightest margin (12 goals/11.52 xG).  

Goals scored excluding penalties compared to xG in 2018 K League leading scorers

It is also interesting to note that runaway league champions Jeonbuk had three of the top nine scorers, but none who significantly outperformed their xG. In fact, three of the five players who did outperform their xG finished in the bottom half of the table.

If all the current players of the 2019 season continue scoring at the same rate as they have over the 14 previous weeks, the 13 still involved in the analysis would end in double figures, but none of them would reach the number of goals scored by Uroš Đerić.

Coaching Considerations

Over the course of the season it is not essential to have a runaway goal scorer who outperforms their xG to challenge for the K League title. Having several reliable players in front of goal can help a team reach the league's summit.

Also, though a player may be scoring the most goals in the team, it does not necessarily mean he is performing well, he may not be making the most of the chances the team is creating for him, meaning the player needs to work on certain finishing scenarios or be replaced with a more efficient finisher.

Using xG alone as a method to analyse a player's performance does not show the quality or quantity of chances a player is getting. If a player has a high quantity of low return shots they could have a similar xG as a player with one higher quality chance.

Part 3: Performance per 90 Minutes

As well as converting on chances created, it is important to look at how many chances players are getting per 90 minutes and their goals per 90 minutes. Though a player may be efficient in converting the chances they get, the best players will get more chances per game. Chances obviously depend on the performance of teammates and tactics but through their own creativity, movement, anticipation, athletic ability and fitness top players get more chances.

Looking at a players performance per 90 minutes on the field also helps factor in injuries, being rested for other tournaments, or international duty. 

K League leading scorers goals per 90 minutes after Round 14.

When looking at goal scoring rates per 90 minutes played, Bae Ki-jong of Gyeongnam FC is averaging more than one goal per game and Daegu FC's Kim Jin-hyeok has also significantly moved up the table. This suggests that they have either been injured or are not a regular fixture in their team's starting eleven. It could be expected that their performance over the course of the season in terms of goal return my drop away and that they have been in an unusual hot streak in front of goal. Simply using the standard goal scoring chart to assess the importance of players to a team can be misleading.

Edgar and Cesinha have both been instrumental in Daegu's rise over the last couple of seasons.

It is also interesting to see that Edgar Silva has risen above Cesinha in this format. Previously we saw how so far this season Edgar has actually been wasteful in front of goal, but this way of looking at his goal return suggests he has a big impact on the teams performance as he has scored at a faster rate than Cesinha and we know he is getting more chances than his fellow countryman. Though his conversion rate has not been where he nor the team would want, his performances on the field results in more goals per 90 and more chances than Cesinha.

By using the previous graph format we can now look at their performances by comparing their goals, minus penalty kicks, per 90 minutes play to their xG per 90 minutes played.

Goals scored per 90 minutes compated to xG per 90 minutes of 2019 K League 1 leading scorers after Round 14

From this graph it is possible to see that Kim Jin-hyeok and Bae Ki-jong are scoring at an unsustainable rate for an entire season, when compared with how the 2018 scorers placed over the 38 games. Kim Shin-wook's early season performances are still impressive, having played lots of minutes, getting a good amount of chances per 90, and converting above average.

When thinking about how a player's season may unfold, we can look at the rate at which they are exceeding their xG. For players wishing to finish as golden boot winners they will need to exceed the average return on the chances they get, whilst playing a lot of minutes and getting numerous high quality chances.

Leading K League 1 scorers' rate which they have over/under performed their xG

Given their low number of minutes played, and exceedingly high rate at which they are out performing their xG, the long term form of Park Yong-ji, Bae Ki-jong and Kim Jin-hyeok could be expected to decline in terms of goal return.

Looking at the rate at which last year's leading scorers exceeded their xG, a performance 20-30% above the average rate of conversion is the high end of goalscorers in the K League.

This draws attention to the current rate at which Pešić and Kim In-sung are converting at. 

They may currently be going through a rich vein of form which could decrease over the course of the season. To keep pace at the top of the charts they may need to receive more chances. Kim Shin-wook's improved finishing this season has seen him score seven goals already, last year he managed 10 in total.

After removing Park Yong-ji, Bae Ki-jong and Kim Jin-hyeok for their exceeding highly rate of conversion over a limited number of minutes played there are five players remaining. Below is a comparison between their conversion rate to xG and their rate over the whole of 2018. The 2018 rate is based on all competitions and players being in different leagues so cannot be considered a direct comparison but gives an idea of the level these players have performed at previously.

Goals scored, xG, and xG in 2018 of leading 2019 K League scorers after Round 14.

An interesting stand out is Ulsan Hyundai's Kim In-sung, although he only scored three league goals last season, he exceeded his xG rate by 45%, and has improved on this rate so far this season to score five goals in 14 games. If he can continue to get into goal scoring positions and receive quality service he could have a very good season in terms of his goal scoring rate.

Coaching Considerations

Looking at a player's performance compared to xG over the long term, even if they are not the team's leading scorers, can help identify players who are accomplished finishers. This may encourage coaches to set up the team to create more opportunities for them or get them into finishing positions more often. It may also show players who are not making the most of the opportunities they get.

When evaluating the performance of goal scorers, using performance versus xG over time or different seasons can help show if a player's recent performance is a temporary improvement in form or a sign of progress in their development as a player.

Part 4: Value of Chances

Another way elite level players differentiate themselves is the amount of shooting opportunities they get per game, and the quality of these opportunities. Through a higher level of anticipation, movement, timing, creativity and technique, the best players find themselves with better quality chances and more often. Being a good striker is not just a matter of finishing the chances you get, but getting more of the better chances than other strikers. 

Think of the common football phrase “being in the right place at the right time”, leading strikers are often associated with knowing where the ball will be before anyone else. They also have moments of individual brilliance, for example Ronaldo's ability to beat defenders one-on-one in dangerous areas of the field to get shooting opportunities.

A player may exceed his xG by converting some low probability chances. Though these goals often stay in the minds of football observers, think of Marco Van Basten's volley in the 1988 UEFA European Championships against the Soviet Union, a player can notsolely rely on continuing to convert these type of opportunities throughout the season.

The table below looks at the amount of open play goals each player has scored, compared to the number of shots they have taken, and then the average xG rate of each shot. A player hoping to continue to score goals and lead the scoring charts would want to be getting a lot of shooting opportunities, with a strong xG average.

Goals scored, shots taken and average xG of 2019 K League scorers after Round 14.

Suwon Bluewings' Adam Taggart has highest average of quality scoring opportunities which bodes well for his chances of maintaining good goal-scoring form throughout the year. Pešić seems to be taking shots from locations or situations that offer a much lower rate of return. This is also concerning as Pešić currently has the most shots, suggesting he may be deciding to shoot at goal at the wrong time, and could be more patient or position himself better on the field.

Adam Taggart made the switch to K League from A-League side Brisbane Roar before the 2019 season.

This method of analysis sheds an interesting light on Edgar Silva. Earlier we saw how Edgar was in good form regarding goals return, created and scored more chances per 90 minutes than his teammates, but was under performing his xG. He had taken 33 shots with an average xG of 0.22. This put him at the same amount of shots as Pešić, but with a much better quality of chance. This would suggest that over the whole of the season Edgar should score more goals than Pešić with only a slight improvement in his conversion rate. If he could equal or exceed his conversion xG he could go on to have an excellent season.

Coaching Considerations

Though short term a player may under or over perform their xG, a closer look at the quality of the chances they have may offer a better insight into their performance and future returns. Memorable goals are fantastic for fans, but converting on a poor quality shooting opportunity can not be relied upon for success over the course of a season.

A players average xG per shot can also be used when looking at the performance of strikers at teams lower in the league. A player may finish the season with less goals than strikers higher up the table due to the quality of his team mates service and teams tactical approach, but if the player is able to find high value opportunities and convert at a decent rate it may be argued that they would perform well in a better team.

Part 5: Future Performances

• Through a closer look at their performance data we can see that Park Yong-ji, Bae Ki-jong and Kim Jin-hyeok are currently going through a hot streak, and are unlikely to end the season near the top of the scoring charts.
• Kim Shin-wook's challenge may fade away in the race for the golden boot when looking at his rate of conversion last season, but he may out score last seasons total.
• Pešić's past performance suggests he will keep scoring but not at this rate, and though he converts at a higher rate than average, he needs to improve the quality of chances he gets.
• Taggart is converting at a rate that, if sustained over the course of the season, would lead him to be near the top of the scoring charts as long continues to have a steady stream of good quality chances.
• Edgar Silva could soon enter a run of good form in front of goal if he can keep up his performances in terms of being on the end of chances. Statistically he is due to start converting more of the chances he gets based upon the average return.
• Kim In-sung converts chances at a good rate, and did so last year, however, he would need to get into more goal scoring situations if he wanted to challenge for the golden boot. His role as a winger means that he may be able to do this to some degree, but possibly not enough to lead the charts.
• Kim Ji-hyun is out performing his xG and did so by an even larger margin last year, however his limited minutes and pending military service means he is a player with long term potential rather than someone a team could look to immediately.
• Junior Negao has a good number of goals already this season, though has under performed his xG. Last season he managed 19 goals and out performed his xG by a healthy 27%. Ulsan are still creating a good number of quality chances for him this season, if he can get back to last years level of finishing he could well be this years K League leading scorer.
• Jeonbuk claimed last years title without a particularly deadly finisher, though they had three players reach double figures in goals, none of them were above the average rate of conversion. A team that can create a high number of good quality of chances and have a range of players converting at an average rate can win the title.
• The struggles of Incheon United may be connected to the sale of Moon Seon-min and the lack of chances created for Mugoša, who is still out performing his xG but has had very limited chances.
• K League leading scorers tend to outperform xG somewhere between 20-30%, how does this compare to other leagues?
• Is there a significant change in the levels of plays xG following the split in the league towards the end of the campaign?

Part 6: Conclusions

• Analysing the performance of goal scorers can not be done through simple goal scoring charts.
• A players xG, their under/over performance of that xG, performance per 90 minutes, shots and average xG per shot can paint a much clearer picture of a strikers performance.
• A team's style of play, and the ability of teammates to create goal scoring chances, are not reflected in this sort of analysis and can have a large bearing on the perceived ability of a striker.
• xG can help coaches identify potential areas where individual players consistently struggle to convert at a below average rate and could focus coaching/training on these areas or adjust style of play.
• The value in xG comes in long term analysis, wonder goals or freak misses can through out a players performance when compared to xG in the short term, but using it as a tool to see a clearer picture of players performance is best applied over longer periods