Tuesday, November 26, 2013

New Jersey Home/Road Split: Undercounting or Style of Play?

Home/road goalie splits for the New Jersey Devils this season:

Home:  .942 Save %, 20.98 SA/60
Road:  .910 Save %, 27.12 SA/60

A difference of 6 shots per 60 is a massive gap, and likely is at least partly due to some small sample size randomness.  However, New Jersey has long been suspected of undercounting shots at their home rink.  What is curious, however, is that the team save percentage is much higher at home than on the road, which is not what would be expected if it was purely a scorer counting issue (see, for example, Martin Brodeur's career splits, which work out to .911 at home vs. .914 on the road, numbers more consistent with a theory of systemic undercounting).

Extra Skater gives possession data at the team level, and those stats indicate that New Jersey is the lowest-event team in the league no matter where their games take place:

Most Low Event Home Teams (Combined Fenwick events per 60 minutes):
1. New Jersey, 58.2
2. Minnesota, 70.9
3. Buffalo, 73.6
4. Columbus, 74.0
5. Calgary, 75.4

Most Low Event Road Teams (Combined Fenwick events per 60):
1. New Jersey, 71.3
2. Edmonton, 74.7
3. Pittsburgh, 74.7
4. Minnesota, 74.7
5. Columbus, 76.9

It certainly seems possible there is some undercounting still going on in New Jersey since they come in so far below all other teams in home Fenwick events, although it should be noted that there were two other teams that had a similar split in terms of a much lower game pace at home compared to on the road.  The Devils' differential of 13.1 only narrowly edged out Ottawa's 12.3 and Buffalo's 11.8.

It is also interesting that the Sabres and Senators have very different goaltending splits during 5 on 5 play (although these are very tiny sample sizes):

Buffalo:  .906 at home, .934 on the road
Ottawa:  .911 at home, .940 on the road
New Jersey:  .931 at home, .911 on the road

The two most common explanations for a team giving up far more shots on the road would seem to be either a difference in the way shots are counted or a team trying to lower average shot quality by giving up more ice from the less dangerous areas of the defensive zone.  Either way, what you expect to see is that the team's goalies do a little bit better on the road than expected, which is again why the Devils' splits seem abnormal.

Looking at the overall population, there is some correlation between pace and save percentage in 2013-14, although it should be noted that the data shows little relationship for 2012-13.  The teams with notably different home/road splits are also quite different from 2012-13 (New Jersey had a difference of just 2.3, albeit in the same direction), with only Carolina and Dallas coming in as substantial outliers over both seasons (both of them playing with a higher pace at home than on the road).

More evidence is needed to show whether a team's pace has any kind of sustained impact on its percentages (in general it probably doesn't), but while they are no longer using the infamous neutral zone trap, it is clear that the New Jersey Devils are focusing more than any team at suppressing shots and chances at both ends of the rink.

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