There's a nice update
to the Shot Quality analysis by Ken Krzywicki over at Hockey Analytics
that's been posted recently, and update based on the 2005-6 NHL
Regular Season data that I've been digging into here. Besides the previous work which looked at shot distance, shot type, rebound situation, and team strength, he's also added Shot After Turnover (based on Takeaways & Giveaways) as a factor in the analysis. It's well worth looking into, and since I was just going to start a similar line of analysis over here, I forwarded some questions over to Ken, which I'll include here:
1) Shouldn't empty-net goals be excluded from the model? The whole notion of shot quality presumes a goaltender on the other end attempting to make a save. For 2005-6 (based on PBP files) I show 7,428 goals, with 178 empty netters. That's around 2.5% enough, to tweak the margins a bit.
2) Should penalty shots be split out as a descriminating factor? Certainly the scenario is somewhat different than the rest of in-game action, and I show 35 penalty shot goals on 85 shots, reflecting a shot quality that is higher than mere distance and shot type would predict.
3) What to do about Missed Shots? While they shouldn't factor into goaltending evaluations, I would think they should certainly count against an offense. There are lots of defensemen with big slapshots that go booming off the endboards, and I would think those should be assigned a zero or near-zero Shot Quality. If you have two players with equal numbers, but one took twice as many Missed Shots as the other, I would think that should reflect in their Shot Quality. You could also give credit to a team defense for higher levels of Missed Shots (not giving opposing shooters enough time & space to shoot well).
4) When looking at Shot After Turnover, should a time constraint be used to ensure that the shot is somewhat related to the turnover? Realistically, after 5 or 10 seconds, the short-term effect of the turnover has pretty much passed as the rest of the players react. I would also add Hits into that filter (i.e. a Takeaway, Hit, or opponent's Giveaway followed by a shot within 10 seconds). For instance, right in the first game of the 2005-6 Regular Season, plays 2 & 3 show a hit by Patrice Bergeron of Boston, followed by a Hal Gill wrist shot 9 seconds later. You could argue that the Hit led to the shot just as surely as a Takeaway would.
Overall, this is a nice update to a very useful piece of analysis by the gang at Hockey Analytics. I've got a slightly different spin on the anlaysis which I hope to post here next week.