Goals by numbers: An analysis of Premier League goal scorers
A very famous person once said, “Statistics are like miniskirts. What they reveal is tantalizing, but what they hide is crucial.” In football, while the basic stats tell you half the story, it is the other half which is all the more interesting. While goals scored and minutes per goal will give you a basic understanding of a striker’s prowess, a little nudge and the Pandora’s Box breaks open revealing much more than what you’d have wished to see. One fine afternoon, I decided to analyze data regarding goals scored in Premier League in a little more detail, or in other words, “take the data down into the basement and torture them until they confess.”
For purpose of simplicity, my data set is limited to the Premier League players who scored 7 or more goals this season or players who are the highest goal scorers of their respective clubs. The basic stats are as follows:
Notice how only 3 players have scored a goal under every 100 minutes they play? No surprises there, given that Luis Suarez, Sergio Aguero and Daniel Sturridge have managed to keep the scorers busy through the season. The advantage of using minutes per goal as a metric to assess goal-scorers is that it removes the effect of time spent on the pitch, or so you would think. While it does not make any considerable difference among the Top 3, it does bring in a sense of perspective as you move from left to right. For example, even though Emmanuel Adebayor has scored only 5 goals, he scores a goal every 146 minutes. Compare this with Rickie Lambert who has scored 7 goals, though scoring a goal every 248 minutes.
Let’s try something else altogether. In simplistic terms, let us try to understand the importance of the goals scored by each of these players to their respective teams. An easy way to visualize it is to take the goals scored by the player as a percentage of the goals scored by the team. If the goals scored by a player do not make a considerable difference, then it can be assumed that the player is disposable.
Luis Suarez has so far scored a whopping 40% of Liverpool’s goals this season. Surprisingly, Sergio Aguero’s goal tally contributes only to 22% of Manchester City’s total. To put things in perspective, Sergio Aguero’s influence on Manchester City’s goal tally is less than Loic Remy, Jay Rodriguez, Charlie Adam, Marouane Chamakh and Adam Johnson among others, though this can be explained by the fact that Edin Dzeko, Alvaro Negredo and Yaya Toure figure among the top scorers of the league. It also dictates that Manchester City should not be affected much by the absence of Sergio Aguero, at least in terms of goals.
The number of goals scored is one metric of comparing goal scorers. Let us try something a little different. How about the number of games a particular player has scored in? Common sense dictates that a superior player would score in more matches than a relatively inferior one. Let us try and plot this metric against the number of games the player has played in for at least 10 minutes (to offset the effect of 88th minute substitutions).
Now the stats start getting interesting. You can clearly see that Daniel Sturridge has scored in 13 matches. Considering he has played only in 16 matches this season, that’s a chance conversion ratio of 81%. Similarly, Sergio Aguero scores in over 70% of the matches he plays in, while Luis Suarez has a ratio of just over 60%. It is interesting to note that Robin van Persie scores in more than 3 out of 5 games he plays in, which goes on to show the importance of the forward in the Manchester United set up.
Conventional statistical models assume that all goals are of equal importance. Any football fan worth his salt would tell you that it’s not true. For the remaining part of the article, I have defined a key goal as follows:
A key goal is that which changes the result of the match when it is scored as compared to before the goal was scored.
Hence, a key goal could be the first goal of the match, a goal which forces a draw or a goal which breaks a draw at any point in the game. It is not a perfect measure, because for a team trailing by 2 goals, each of the comeback goals is equally important. For sake of simplicity, we assume the above condition though. Hence, Sturridge’s first goal against Aston Villa does not count as a key goal, in this article. Also, for the remaining part of the article, we are considering only players who have scored in at least 6 matches.
Sergio Aguero has scored the most number of key goals – 8 key goals, which is a respectable 53% of his total tally. He is closely followed by the Liverpool duo of Luis Suarez and Daniel Sturridge, Olivier Giroud and Eden Hazard at 7 key goals. It is worth noting that it comprises of only 30% of Luis Suarez’ total goals, meaning over two-thirds of his goals had no impact on the match result at the moment they were scored. On the other hand, 78% of Eden Hazard’s goals were match-changing ones. The stat in itself does not tell us much, apart from the fact that Luis Suarez scores a larger proportion of his goals when the pressure is off him and Eden Hazard, when there is pressure is on him to make a difference to the match. The reasons may range from the opposition tactics to the player’s mentality to performance of the player’s team mates; no conclusion could be drawn from merely these statistics. For example, a lot of Sergio Aguero’s key goals happen to be the first goal of the game, and it has a lot to do with Manchester City’s attacking play than anything else.
To demonstrate the above mentioned point in a different way, the graph below shows the number of key goals against minutes per key goal. The trend is smoother in this graph as compared to the earlier one.
Sergio Aguero leads in this metric, with a key goal every 149 minutes, followed by Robin van Persie with a key goal every 175 minutes, or in under 2 games. The statistic throws an interesting proposition – had Robin van Persie played more this season, things might have been different for Manchester United. Luis Suarez performs marginally better than the previous metric, with a key goal every 244 minutes, with his strike partner Daniel Sturridge with a key goal every 2 games. It is worth noting that Edin Dzeko has a higher proportion of his goals being key goals than Alvaro Negredo, and scores key goals (and goals) at a higher rate than the Spaniard. Manuel Pellegrini might do well to play Edin Dzeko more often, especially when the result needs to be influenced, going by the model.
Finally, let us look at the playing style of these players. For that purpose, I plotted the Total shots and accuracy for each player and obtained the following graph.
Nothing really springs out from this graph except Luis Suarez’ high number of shots – 103 shots, which is a good 42 shots more than the next player, and Olivier Giroud’s extremely average shot accuracy of 40%. Aaron Ramsey does well to get more than 70% of his shots on target, a good figure for a midfielder. This is not a very good stat to judge a goal scorer by, hence we need to look at something more conclusive.
So let us try it again using slightly different metrics – shots per 90 minutes and shots per goal scored. The graph gets interesting.
It should be clear by now that the ridiculously high number of shots by Luis Suarez was only due to the time he spent on pitch and not anything else. Sergio Aguero averages almost just as many shots in 90 minutes (5.29) as Luis Suarez (5.49). They also take around as many shots as each other to score a goal. The really interesting part of this graph is towards the right end though, where Yaya Toure scores a goal every 3 shots he takes. With a shot per 90 minutes value of 1.67, it means that Yaya Toure scores a goal in under every 2 full games he is on the pitch – the best returns for any midfielder. What’s even better, the stat tells you that he scores 0.66 goals every shot on target, that is 2 goals every 3 shots on target!
I will end this article with the key stats of players under consideration from the Big 5 teams, which might give you some insights into why some teams are performing better than the others, and if some players are as indispensable to their teams as you think.
All this while, the analysis was purely based on considering the players to be nothing more than goal scorers, which is not a definitive approach to rating the players. But this provides a decent enough platform to understand player trends at a single glance, and models would be built on this using more relevant data and extensive analysis.
Take this article with a lump of salt, if by chance your favorite player does not figure favorably in it. After all, like Mark Twain said, “Get your facts first, and then you can distort them as much as you please.”
If you are a stat enthusiast and would like to see the datasheet, you may download it here.