Monday, June 8, 2009

Scoring Chances by Game State

For those that aren't aware, Dennis King, one of the posters at, took the time to track scoring chances for the Oilers over the course of the 08-09 NHL season. An example.

The work that he did is really quite impressive -- for every game, Dennis managed to record the scoring chances for each team, the time that the scoring chance occurred at, which players were on the ice when the scoring chance occurred, and game for and against totals for every Oiler player.

Needless to say, to do that for an entire season is no small task, and Dennis deserves some major credit for all the work that he put into the project.

For those interested, Scott Reynolds at GospelofHockey has made some interesting posts on the subject, as has Vic Ferrari (see here and here, for a few examples).

The topic of this post, however, is whether scoring chances differ according to game state. The term game state is a little vague -- in this case, I'm using the term to refer to whether or not the score was tied at the time the scoring chance happened. In other words, is there a 'playing to the score effect' in terms of scoring chances?

Prior to examining the results, I wasn't sure what to anticipate. On the one hand, shot ratio does vary according to the score, and the effect is fairly marked. As scoring chances are (highly) correlated with shots on goal, intuitively one might expect a parallel effect on scoring chance numbers.

On the other hand, there are reasons to expect a more moderate effect. The team that is playing from behind often plays quite desperately in an attempt to avoid losing. Consequently, the trailing team tends to be more liberal in its shot selection and, on account of playing more aggressively, is forced to concede a high frequency of odd-man rushes against.

Using the data provided by Dennis, I've looked at how the Oilers scoring chance numbers varied according to game state -- that is, whether they were trailing, tied, or leading at the time the scoring chance happened.

I've presented the overall results -- that is, the results for every game situation (EV, PP, SH), as well as the results at even strength only.

I've also added a second table that breaks down the data by period.

I should note that this data is only for 49 of the 77 games that Dennis tracked scoring chances for -- I wasn't able to easily cut and paste the first 30 or so games into excel. Nonetheless, I think that 49 games provides an adequate sample size.

The results:

The abbreviations in each column, from left to right, stand for: scoring chances for, scoring chances against, goals for, goals against, scoring chances for per goal, scoring chances against per goal, time on ice, scoring chances for per minute, scoring chances against per minute.

I was unable to determine time on ice values for even strength due to the way in which the data was recorded.

Some observations:

1. In a recent post on shot ratio by goal state, Tyler at mc79hockey remarked that he wasn't convinced that sitting on the lead was a good strategy. I'm inclined to agree with him. The Oilers were solidly outchanced when playing with the lead, both at even strength and otherwise, and were outscored just as badly.

Likewise , Edmonton actually outchanced the opposition when playing from behind, albeit narrowly.

2. There isn't much evidence that scoring chance quality varies by game state. One might have predicted that the leading team would capitalize on a higher percentage of its scoring chances. However, that doesn't appear to be the case. The team that was leading tended to capitalize on a higher percentage of its scoring chances at even strength, but the difference is quite small and probably not statistically significant.

3. It's difficult to say whether or not the effect is more pronounced later in the game. This was certainly the case when the Oilers were trailing. However, when leading, the opposition decidedly outchanced the Oilers regardless of the period.