February 20 2013 11:18AM
Image courtesy Shaun Kreider, Kreider Designs
NHL Numbers previously published a couple of articles on zone entry tracking. We first looked at the results in Flyers games from 2011-12, observing that shot differential at 5-on-5 appears to be largely determined by neutral zone play, and that retaining possession as a team enters the offensive zone is particularly important, generating more than twice as much offense as a dump-and-chase play.
We then called for volunteers to join the project and have had a number of people contribute. We have expanded our database to include a full season of data from the Wild, a half-season of data from the Sabres, a half-season of data from the Capitals, and over 100 assorted games from other teams in 2011-12. This has allowed us to further generalize and strengthen our conclusions for a paper that will be presented at the MIT Sloan Sports Analytics Conference.
One unique wrinkle in the new data is that for the first time, we have tracked failed zone entries. Previously, we had inferred that teams should be more aggressive at the blue line, that the benefits of carrying the puck in were large enough that it was worth the risk. Now we have the data directly to assess how likely it is that a blue line turnover gets turned around the other way and how many shots result from that play. The result is the following decision matrix, taken from that paper:
The solid blue line represents the boundary between when a player should try to carry the puck in or when he should dump it in if the two teams are roughly equal. So on a given play, imagine you are carrying the puck up the ice towards the opposing blue line. If you think successfully gaining the zone would result in a typical ~0.56 shots (the dotted grey line), then you should challenge the defense if you think it's better than roughly one-in-three that you'll beat them and gain the zone.
If your skaters are good shooters (or the opposing goalie is bad) and your opponents are bad shooters (or your goalie is good), then getting extra shots for you has more benefit and turning it over carries less risk. So then instead of using the solid blue line, you can use the dashed blue line, which shows the cutoff for a team whose shooters score on 9% of their shots on goal and save 93% of the opponents' shots. This would allow you to be even more aggressive, and test the defense even when they are so well set up that you expect them to break up the play three out of four times.
When you watch a game, keep an eye on how often teams carry the puck into the offensive zone. You'll find that the players who really drive possession are the ones who are aggressive at the blue lines, and that teams in general seem far too willing to dump the puck in, making the seemingly conservative play that actually costs them in the long run.