Chelsea: Using data to assess the quality of the Blues’ created chances

Chelsea hasn’t scored as many goals as fans would’ve hoped this season for multiple reasons, but are the Blues’ chances quality ones?

Chance creation is like the lifeblood of a team’s attacking potency. It is what get’s fans, pundits, coaches off their seat. That moment of a chance being created is when the crowd unites into a state of anticipation and hope

In this article, we take a look at how to assess the chance creation ability of Chelsea’s players based on last season’s performance. Chance creation, according to Sam Gregory, a Statsbomb analytics writer, consists of two main actions: a shot and the pass that directly lead to that shot.

Assessing Chance Creation

Chance Creation is defined using a very specific equation, shots-per 90 + shot/assist per 90. However, not all shots and chances are created equally. Thus, it is useful to weigh these numbers by the assist rate, or assists/shot assists, and the scoring rate, goals/shots. Then, we can find a weighted chance creation by using shots assists per 90 x (1 + assist rate) + shots per 90 x (1 + shot rate).

Using these calculations the Chelsea player’s chance creation ability can be ranked to get a better understanding of which players are the best at creating chances.

*snapshot of the table (similar calculation done for the whole squad)

* data for last season

The tables above has the player’s statistics required to perform this calculation including goals, assists, total shots, shots per 90 and shot assists per 90. Based on these numbers the assist rate, shot assists per 90 adj (SAp90) and Shot per 90 adj(SP90 adj) are calculated.

Take a look at Ziyech’s Chance creation score. First, let’s take a look at this shot per 90 adjusted number based on his scoring rate:

"S90 (Shot 90 adjusted) =  Ziyech’s Shot per 90 ( Last season) * (1 + Ziyech’s Scoring rate)Ziyech’s Scoring  rate = Ziyech number of goals /Ziyech Total number of shots"

Since his shot rate (i.e. shot conversion rate into goals) is only four percent, his 4.1 shots per 90 adjusted for scoring rate is only 0.2. This is in line with what we know about Ziyech; he takes a lot of unnecessary shots which often leads to a turnover in possession. Whilst this is somewhat acceptable in the Eredivisie, in the Premier League, this could be costly in terms of being susceptible to counter attacks or losing the opportunity to find a better scoring opportunity.

The same is then done for shot assists adjusted per 90 based on his assist rate. The two numbers are then added up to get a weighted chance creation (WCC) number.

Ziyech is on top of the list due to his unreal assist rate with approximately 16 percent of his shot assists leading to goals. Of course, that need’s to discounted as it might not be as easy to maintain the same output in the premier league. Still, formidable numbers, if he can bring even half of that output to the Blues it would be a significant upgrade to any other player in terms of chance creation.

The WCC can then be normalized to get a score between one and a 100 to assess a chance creation score. This is in reference to the rest of the Chelsea players. Since Ziyech’s score was highest he gets a score of a 100 and the rest of the players’ scores are calculated in reference.

Timo Werner comes in second due to his prolific scoring rate. Callum Hudson-Odoi is surprisingly third though he did play far fewer minutes than most of the other players. Ross Barkley (since loaned to Aston Villa) is again high up on the list due to a lower sample of minutes played.

Other than that the rest of the list looks reasonable as we all know what great seasons Christian Pulisic, Kai Havertz, Mason Mount and Ben Chilwell had last season.

Finally, we can take the average rating score and assess if the players are above or below the average rating for chance creation.

Conclusion

There are oversimplification and assumptions made by these calculations, however, at its essence, it makes sense to assess a player’s chance creation ability based on shots-per 90 adjusted for scoring rate and shot assists per 90 adjusted for assist rate to get a sense of how vital the player is to make things happen for the Blues. Further, since the assist and scoring rates based on an entire season’s worth of data the sample size is large enough to minimize any noise that exists in the weights.

The Wizard of Amsterdam has high expectations on his shoulder to create chances. Whilst Havertz, Mount, Pulisic and Werner are all exciting players, Ziyech is arguably the most experienced creator. Let’s hope he can adapt well to the Premier League and be the man who enables the Blues’ other exciting young talents to maximize their potential.

All data is from Wyscout. The model is adapted from Sam Gregory’s Statsbomb model. For further information on the calculations, reach out on Twitter!