Chelsea has scored just six league goals since November 6, 2022 (12 league games). The question ‘how crucial are big chances?’ is very much tied into the expected goals (xG) debate and how reliable it is as a model. Many claim most xG models are incomplete. The fact remains that many users of xG don’t know how to use it, and keep trying to use it for what it wasn’t meant for. xG can be measured for players, but can also be measured for teams, and today we’d be focusing on the latter.
The reason xG is important is because big chances are defined by xG value, amongst other things. Opta defines it best, but a big chance is a chance where a player is favoured to score with respect to the goalkeeper. The big chance definition takes into consideration the position the shot is taken from, the path of the ball to the goal and the amount of pressure on the player shooting the ball. Therefore, a big chance has a minimum xG value of 0.25.
This means the average player is expected to score a big chance 25 per cent of the time. The player in “average player” refers to any player, not just forwards or strikers. A good big chance conversion rate for a striker would be 40-45%, the best finishers hover around the 47-55% range over a full season when you consider shots taken and goals scored. Anything above 55% is outrageous.
It should be mentioned that the more big chances a player gets, the more likely their conversion rate would reduce over the course of a season. We now know what a big chance is, and what big chance conversion should look like for players. But how should they look like for teams? Why are they important? Why should teams strife to create as much as they can? Shouldn’t they just focus on getting goals wherever they can, regardless of whether it’s from a big chance or not? Should players not just be better at shooting the ball when their teams aren’t creating many big chances? Should teams not just get better shooters when they’re struggling to score?
First of all, the largest proportion of a team’s goals usually come from converting big chances, especially non-penalty big chances. A team would typically get 99% of their goals from non-penalty big chances, penalties, or non-big chances (usually called half chances). They also get goals from own goals, but those are so few that they’re negligible for the sake of this piece. If scoring from non-penalty big chances are one source of goals, penalties are another and half chances are another, a higher proportion of a team’s goals should typically come from big chances. Teams should then strife to create as many big chances because it usually increases the numbers of goals they’d score.
Looking at the proportion of goals from various sources for 14 teams across Europe’s top five leagues. Manchester City, Arsenal, Chelsea, Tottenham, Real Madrid, FC Barcelona, Bayern Munich, RB Leipzig, SSC Napoli, AS Roma, Paris Saint Germain, Marseille, and Toulouse. Before examining the results, it should be noted that these figures were calculated with a minimum xG value of 0.25 for big chances, which means that when examining xG from big chances as opposed to xG from half chances, the xG from big chances are calculated as though all big chances are exactly 0.25 xG, when in reality, most big chances are higher than 0.25 xG, so the proportion of goals from big chances would actually be a minimum, showing that the actual proportion of xG from big chances is considerably higher.
Of the teams examined, the team with the lowest minimum proportion of goals from non-penalty big chances was Tottenham Hotspur, where non-penalty big chances accounted for 43% of their goals this season as at Matchday 21. At the top of that list is FC Barcelona, where non-penalty big chances account for 79% of their league goals this season. At Napoli, it accounts for 61% of their goals and at Manchester City it accounts for 59% of their goals. At Arsenal it accounts for 51%. These numbers obviously vary, as different clubs have players with different skill levels of finishing. These numbers are more defining when you consider that big chances account for a very small percentage of the shots a team takes.
At Spurs, big chances account for 15% of their shots, which means that from 15% of the shots they take comes 43% of their goals. The important of big chances become clear. At Barcelona, from 23% their shots comes 79% of their goals. At Manchester City from 21% comes 59% and at Napoli from 17% comes 61%. The varying of the numbers aren’t worth paying attention to, what is glaring is that a relatively small percentage of a teams chances are big chances, but at the same time it’s from those big chances that the bulk of their goals would come from, so the more of those big chances they can create, the more goals they’d be able to score.
This does not just apply to actual goals, but expected goals too. Using the same five clubs mentioned above, non-penalty big chances account for at least 32% of their total xG. Again, note that the actual figure would be way higher because very few big chances are actually 0.25 xG. At Barcelona non-penalty big chances account for at least 42% of their xG, for Napoli and Arsenal it’s 34%, and for Manchester City it’s 40%. Again, the numbers vary because every team is different, but the point still stands. At Barcelona, 23% of their shots account for 42% of their xG and 79% of their goals. Seems like an extremely important 23%. And the 23% are the big chances.
Chelsea has had a problem creating a volume of clear cut chances befitting for the amount of the ball they get per game. This season it has been much worse. 46% of Chelsea’s goals this season are from non-penalty big chances. 17% of their shots are from big chances, and 39% of their xG are from non-penalty big chances. This is normal, in terms of proportions, but what makes it a problem, is the number of big chances it has created relative to some other teams in Europe.
Chelsea, as at the writing of this piece, has created 41 clear cut chances in 21 games. For a team that control 59% of the ball in every game without fail, that’s really poor. The Blues don’t have bad strikers, they just have starving strikers. Their goals are coming from where you’d typically want them to come from, but there just isn’t much to draw from. Toulouse, a newly-promoted team in the Ligue 1 has created 12 more big chances in the same amount of games. This is poor from Chelsea.
This inability to get goals, is also something that Chelsea head coach Graham Potter suffered in all three seasons at Brighton as well, in his last full season at Brighton he was only able to distribute the goals better to finish 9th in the Premier League. This scoring problem was traceable to a lack of big chances as well. In Potter’s highest ever league finish with Brighton, the seagulls created 12.9 chances per game, 489 chances in all. They only created 61 big chances though, which accounted for 12% of their shots. From that 12%, they scored 45% of their league goals, which is normal.
There’s a narrative that Potter’s Brighton team usually underperformed their xG and those teams just had finishing issues, but his team finished chances fine, they just didn’t create enough of the good chances. This is not just true for his last season at Brighton, but his first and second too. In the 2020/21 season, big chances accounted for 13% of Brighton’s shots, and from that came 48% of their league goals. These figures were worse in his first season at Brighton, as from 13% of their shots came 28% of their goals. Potter’s Brighton didn’t underperform as much as was reported, they just struggled to create enough good chances. This is the same problem his Chelsea team is having. xG numbers are primarily from fbref, big chance numbers are primarily from Sofascore