Why Chelsea score so few goals and how crucial big chances are

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.