Advanced Hockey Stats Introduction: Corsi, Corsi Relative, Fenwick, Etc.

We, as hockey fans, know that puck possession is a critical factor in a hockey game.  We also are all familiar with the plus-minus stat in the game.  Corsi is basically a plus-minus stat that is a proxy for puck possession.  Below is a good explanation of what exactly Corsi is from Matchsticks and Gasoline:

At its most basic level, Corsi is the plus/minus amount of shots directed at a net while at even strength-blocked shots, shots high and wide, shots that hit, shots that get tipped, etc. A player who has a positive Corsi has more shots directed towards the opponents net while he is on the ice at even strength then shots directed towards his own net under the same criteria. All 10 players on the ice are used when calculating this metric.

So let's say Patrick Sharp had a Corsi rating of +6 against Detroit one night.  This means that when Sharp was on the ice, he and his teammates (on the ice with him) shot the puck 6 more times at Detroit's net than Detroit shot at the Hawks'.  If Sharp had a -6 rating, this would imply the opposite.

Notice that even if the shot is blocked or isn't on goal, it is still counted toward Corsi.  Why is this? Because even if it was missed, the team still had to have possession in order to shoot it.  Again, Corsi is a proxy for puck possession.

Now there are also other forms of Corsi which I'll get to below.

The first is Corsi Relative.  Corsi Relative is, well...relative because good teams will usually dominate puck possession and shots.  Therefore the stats for players on good teams will be inflated a little.  Corsi Relative is the Corsi of a specific player minus the Corsi of his team when he is not on the ice per 60 minutes.  Last year, Patrick Sharp led the Blackhawks in Corsi Relative at +15.

Next is Corsi Rel QoC.  Because specific players are going to be matched up against the other team's best, their Corsi rating may be a bit skewed.  Relative Corsi Quality of Competition (Corsi Rel QoC) measures the strength of the competition the player is going up against.  It is the Relative Corsi of a player's opponents.  Who faced the toughest competition last year for the Blackhawks?  Brent Seabrook did with a Corsi Rel QoC of 1.522.  Considering Seabrook managed the 7th-highest Corsi Relative (minimum of 40 games) on the team yet faced the hardest competition is impressive.

Now as I've stated above, Corsi includes block shots.  Matt Fenwick from Battle of Alberta didn't like that and came up with is own stat; Fenwick.  Fenwick is the exactly the same as Corsi except it excludes blocked shots as it is a skill.  I will still use Fenwick in this blog, but I agree with Adnan over at Silver Seven in that I prefer Corsi because you are still in the offensive zone and still had enough space to generate a shot.

Anyway, those are the main puck possession stats we will be covering here at BH.  If you have any questions, leave a comment below.