Friday, 5 April 2013

The Impact of Big Chance Conversion

At the end of last season I compared the top scorers in the Premier League using the MCFC Analytics data, one of the things missing however was goals scored via 'Big Chances' (defined as a chance where a player would reasonably be expected to score).

This season, using data from EPL Index, I've been able to look at the impact of Big Chances and have used that to look at the scoring behaviour of some of the Premier Leagues top scorers as well as discovering some huge differences in Big Chance conversion rates between teams.

As at 5th April, there were 22 players who had scored 10 or more Premier League goals:
Players with 10+ Premier League goals, some such as Berbatov and Lampard have a significant proportion of goals via penalties
The initial part of this analysis will look at the top 4 on the list (Suarez, van Persie, Bale and Michu):
In terms of Minutes Played, Suarez has played the equivalent of around 2 full games more than Michu and 3 more than RvP/Bale as well as having had far more shots
When breaking those shots down in to more detail, it can be seen that Suarez has a far higher proportion of shots that are blocked and Michu a higher proportion that are off-target:
Suarez and Michu have approx. a third of their shots hit the target compared to closer to half for RvP/Bale
Not all chances are the same which is where breaking shots down into Big/Other chances helps give more understanding as to how players are performing:
Top 4 Scorers and PL as a whole.  Goals figures exclude Own Goals, Big Chance and Other Attempts figures exclude penalties
From the figures it can be seen that these 4 players are the top scorers for different reasons:

  • Suarez - Excellent Big Chance conversion rate coupled with a few goals from a glut of shots
  • van Persie - Average Big Chance conversion rate but has had the most Big Chances of any player, good conversion of other chances
  • Bale - Excellent Big Chance conversion (but few chances), good conversion of other chances across a large number of attempts
  • Michu - Excellent Big Chance conversion with an OK conversion of other attempts
As a comparison Suarez only scored 25% of his Big Chances last season (7 of 28), with van Persie scoring 46% (21 of 46) and Bale 33% (3 from 9).

When looking at goals scored which are relatively rare compared to passes for example, there's always more room for differences in performance to be due to chance rather than a real difference. 7 of Bale's 17 goals have come from outside the area but you could argue he's done it often enough to show it's not a fluke:
Location of Goals from Bale (via Squawka)
As well as the top players there are few other players who have interesting stats around chance conversion:
Range of Players with stand out figures for a range of reasons (good and bad)
It's off a small sample size, but it was interesting to see the poor Big Chance conversion rate for Jelavic and Adebayor, both of whom did well last season (with Big Chance conversion rates of 43% and 41% respectively).

Giroud has very similar stats to Michu in terms of total shots/Big Chances with one very important difference:  Michu has converted 52% of his 21 Big Chances compared to just 19% from Giroud.  It's an almighty if, but if Giroud can convert his Big Chances at the same rate as Suarez/Michu have done this season then he'd probably get around 20 league goals given the number of chances Arsenal create.

Mata is arguably one of the most technically gifted players in the league and his conversion rate of non-Big Chances stands out at almost 15%.

I was under the impression that Pogrebnyak was having a disappointing season at Reading but looking at the stats, purely in terms of taking chances he's not got bad figures.  Looking at a team level however you can start to see why he hasn't scored too many.
Big Chances by Team
Reading have the lowest number of Big Chances created by some distance, but have converted the highest proportion of any team.

Man Utd have created the most Big Chances and also have one of the best conversion rates, in terms of total goals scored this explains most of the difference between them and Man City this season.

Where Reading don't make many chances but convert a good proportion of those they get, West Ham have the opposite problem, creating a decent number but with a terrible conversion rate.
Big Chances Created and Scored by Team - Those below the line have below average conversion rate
No single metric works in isolation from other figures but as almost half of all goals come as a result of Big Chances the value of a finisher is huge, the difficult part is differentiating between the flash-in-the-pan, the consistent goalscorer and the players who might come good again in time.

There's also other issues such as does a side have few clear cut chances because forwards are making bad runs or because the midfield are supplying poor balls.

Related Posts:
A Review of publicly available Opta Data Sources
Premier League Weekly Review
How Mark Gower became 'The most creative player in Europe'
2011/12 Top Scorers by club compared

Twitter: @we_r_pl
Stats and Chalkboards: Created using EPL Index / Squawka