Scoring Goals: Shot Generation or Shooting Percentage?
There are two things that must occur to score a goal. The first way is to get an opportunity to score and the second is to capitalize on that opportunity to score. There are a number of statistics that we can use as a proxy for opportunity to score but one of the most common is Fenwick numbers which are shots + missed shots (some call this Corsi but I define Corsi as shots + missed shots + blocked shots). We can then define the ability to cash in on opportunities as shooting percentage, or in this case fenwick shooting percentage. So let me define the following:
Opportunity Generation = Fenwick shots per 20 minutes of ice time.
Capitalization Ability = Fenwick Shooting Percentage = Goals Scored / Fenwick shots
So the question I pose today is this: What is more important in scoring goals, generating opportunities or the ability to capitalize on those opportunities. To answer this I calculated each teams Fenwick per 20 minutes (opportunity generation) and each teams Fenwick Shooting Percentage (capitalization ability) and compared them to the number of goals they generated per 20 minutes of ice time and I did this for each of the past three seasons (I only considered even strength five on five data). I also did this for both the offensive and defensive ends of the ice for a total of 90 data points offensively and defensively.
First for the offensive end of the game:
As you can see, shooting percentage (opportunity capitalization) has a much stronger relationship with scoring goals than getting shots (opportunity generation). What about the defensive end of the game?
Again, opposition capitalization rates are much more correlated with scoring goals than opportunity generation. In fact opportunity generation appears to have no correlation with giving up goals at.
The conclusion we can draw from these four charts is when it comes to scoring goals, having the ability to capitalize on opportunities (shots) is far more important than having the ability to generate opportunities (getting shots). Controlling the play and generating shots does not mean you’ll score goals (just ask any Maple Leaf fan), having the talent to capitalize on those opportunities is what matters most. From my perspective, this means the usefulness of ‘Corsi Analysis’ to be minimal, at least for the purpose of evaluating players and teams. For evaluating goaltender workload, as it was initially intended by its originator former NHL goalie and Buffalo goalie coach Jim Corsi, it still has merit.