As has been demonstrated clearly in a series of recent articles here, there is little margin in goalie skill in todayís NHL. It is very difficult to differentiate an average goalie and a good goalie through means other than measuring their performance over a large sample of games, with save percentage as the key performance metric. However, save percentage is based on the number of shots and saves recorded by the official scorer in every game played. Some shots are very subjective in terms of whether they are recorded or not. If shots are counted differently from rink to rink this would make it difficult to know whether a small observed margin between two goalies was a result of skill or a home rink advantage.
Tom Awad has demonstrated clearly that for many teams there is a significant difference in the total number of shots taken in home games compared to games that they played on the road. This is certainly suggestive of a variance in the subjectivity of official scorers from rink to rink. However, other investigations of this issue have shown that there may be some evidence that teams change their style of play. For example, JLikens at Objective NHL found that some teams had similar scoring and save percentages both at home and on the road, despite a different overall shot total. This means that simply comparing total shots may not tell the whole story.
Given these findings and the simple fact that some teams have widely divergent home and road records, it seems reasonable that certain teams might either vary their tactics or for whatever reason simply be more effective either at home or on the road. What is missing is a frame of reference. If information was tracked on where the puck is located at all times, it would be easier to determine whether events are being recorded improperly or if the observed events simply became more likely or unlikely as a result of the teamís style of play.
Fortunately, this information is available for three seasons. From 1999-00 to 2001-02, the NHL recorded zone time for each team, and as a result there is available data that tells how much time the puck spent in the offensive, defensive and neutral zones for every team in the league. This should give us the ability to assess with a little more precision whether teams vary their tactics based on where they are playing the game or whether the scorers see things very differently.
I am assuming here that the zone time data itself is not biased. This should be a reasonable assumption because unlike most real-time scoring there is no subjectivity involved in tracking zone time. At any point in time the puck is in one zone and not in the two others. Having said that, a number of game sheets had to be excluded because they either did not include zone time or the numbers were out of realistic range. It is possible that some games included measurement errors, but the bulk of the sample should provide a good set of data for analysis.
On average, the home team had the territorial edge over the three seasons. The puck was in the visiting teamís end 39.3% of the time, compared to 37.9% for the home team. That leaves 22.8% of the time that the puck was in the neutral zone.
For each team from 1999-00 to 2001-02, here are the percentages of time spent in the offensive, neutral and defensive zones, both at home and on the road (note that because of rounding, the percentages may not sum to exactly 100%):
Home Home Home Road Road Road Diff Diff Diff
Team Off Neut Def Off Neut Def Off Neut Def
ANA 39.3% 22.9% 37.8% 37.6% 22.3% 40.1% 1.7% 0.6% -2.4%
ATL 37.0% 20.7% 42.3% 35.9% 22.2% 41.9% 1.1% -1.5% 0.5%
BOS 39.9% 25.3% 34.8% 38.4% 23.5% 38.1% 1.6% 1.8% -3.3%
BUF 39.6% 23.2% 37.2% 38.3% 22.7% 39.0% 1.3% 0.5% -1.8%
CAL 39.2% 22.3% 38.5% 38.0% 22.0% 40.1% 1.3% 0.3% -1.6%
CAR 40.1% 23.5% 36.3% 39.3% 22.6% 38.1% 0.9% 0.9% -1.7%
CHI 39.9% 22.2% 37.9% 38.2% 22.7% 39.1% 1.7% -0.5% -1.2%
COL 38.8% 22.6% 38.5% 36.9% 23.1% 40.0% 1.9% -0.5% -1.4%
CBJ 38.0% 23.8% 38.1% 35.8% 22.0% 42.2% 2.2% 1.8% -4.0%
DAL 40.1% 23.5% 36.4% 39.4% 23.6% 37.0% 0.7% -0.1% -0.6%
DET 40.1% 23.6% 36.3% 38.7% 23.4% 37.8% 1.4% 0.1% -1.5%
EDM 39.7% 22.7% 37.5% 38.7% 21.8% 39.5% 1.0% 0.9% -2.0%
FLA 37.7% 22.4% 39.9% 35.7% 23.2% 41.1% 2.0% -0.8% -1.2%
LAK 40.8% 21.2% 38.0% 38.4% 22.7% 38.9% 2.5% -1.5% -0.9%
MIN 37.1% 22.3% 40.7% 34.7% 22.4% 42.9% 2.3% -0.1% -2.2%
MON 39.0% 22.1% 38.9% 37.4% 23.2% 39.4% 1.6% -1.0% -0.5%
NSH 38.6% 22.0% 39.4% 37.2% 21.8% 41.0% 1.3% 0.2% -1.6%
NJD 39.4% 25.2% 35.4% 38.9% 23.9% 37.2% 0.5% 1.3% -1.8%
NYI 38.6% 23.4% 38.0% 37.7% 22.2% 40.1% 0.9% 1.3% -2.1%
NYR 38.0% 23.9% 38.1% 36.5% 23.1% 40.4% 1.5% 0.9% -2.4%
OTT 40.8% 23.7% 35.5% 40.1% 22.6% 37.4% 0.8% 1.1% -1.9%
PHI 40.5% 21.2% 38.3% 40.0% 23.5% 36.4% 0.4% -2.3% 1.9%
PHX 38.5% 22.4% 39.0% 37.3% 22.0% 40.7% 1.2% 0.4% -1.6%
PIT 38.3% 22.3% 39.4% 36.7% 23.1% 40.2% 1.5% -0.8% -0.7%
SJS 41.3% 22.8% 36.0% 38.8% 22.6% 38.6% 2.4% 0.2% -2.6%
STL 41.3% 21.5% 37.3% 38.2% 25.2% 36.6% 3.1% -3.8% 0.7%
TBL 36.7% 24.1% 39.2% 36.3% 21.9% 41.8% 0.4% 2.2% -2.6%
TOR 39.4% 22.9% 37.7% 37.9% 23.3% 38.7% 1.5% -0.5% -1.0%
VAN 40.1% 23.0% 36.9% 38.9% 23.0% 38.1% 1.2% -0.1% -1.2%
WSH 40.2% 22.1% 37.7% 38.5% 22.7% 38.8% 1.7% -0.6% -1.1%
The neutral zone numbers are probably the most informative. The more conservative a team is playing, the more time the puck is likely to spend in the neutral zone. If the puck spent more time between zones at home, it is likely that the team played a more conservative strategy on their own rink. If the puck was in the neutral zone more often when the team was on the road, they likely opened up their game to entertain the home fans.
Teams that had more neutral zone time at home:
- Tampa Bay, 2.2%
- Boston, 1.8%
- Columbus, 1.8%
- New Jersey, 1.3%
- N.Y. Islanders, 1.3%
Teams that had more neutral zone time on the road:
- St. Louis, -3.8%
- Philadelphia, -2.3%
- Atlanta, -1.5%
- Los Angeles, -1.5%
- Montreal, -1.0%
The Blues were the largest outlier, so much so that it is probably reasonable to question whether their home-town zone time measurement was accurate. On the other hand, the Blues had a terrific defensive team, anchored by Al MacInnis and Chris Pronger, and may have had the ability and/or inclination to play a low-event game on the road. Philadelphia was likely similar in utilizing a more conservative game plan on the road. Atlanta looks to have traded off defense for offense while playing in front of the home fans, likely as an attempt to entertain the home fans and sell more tickets in an expansion market. The Thrashersí home games had the least time spent in the neutral zone of any team in the league.
In contrast, teams like Tampa Bay, Boston, and Columbus probably were more likely to utilize the neutral zone trap or other similar tactics at home than they were on the road. Perhaps those management groups counted on home wins doing more than goals scored to boost attendance.
The potential effect on total shots can be estimated from the zone time figures. The assumption here is that all shots came from play in either the offensive zone or defensive zone. This is of course an unrealistic assumption since shooters sometimes dump in on the net from anywhere on the ice surface, but neutral zone shots are rare and almost certainly a small enough percentage of the total that it should not change the numbers much at all.
League-wide there was an average of 70.8 shots per 60 minutes of time spent in either attacking zone. Given the numbers above that indicate the puck was in either attacking zone 78.6% of the time in St. Louis home games and 74.8% of the time in St. Louis road games, it follows that an average team playing against average opposition would have an expected shot total of 55.6 total shots per game at home and 53.0 shots per game on the road. St. Louisí actual totals were 52.1 total shots per game at home and 53.1 shots per game on the road, which indicates that the official scorer there may have been undercounting.
On the other end of the spectrum, the puck was in either attacking zone 75.9% of the time in Tampa Bay home games and 78.1% of the time when the Lightning went on the road. This gives expected totals of 53.7 shots per game at home and 55.3 shots per game on the road. Tampa Bayís actual numbers were 55.4 and 57.1 respectively. Thatís a very similar shot difference and shots for/against ratio, which suggests that the Tampa scorer may have recorded things accurately and the teamís style of play caused a higher than average number of shots per minute.
It seems clear that some teams played a different style of territorial game on the road. Other teams played with different levels of effectiveness depending on the venue, perhaps because they were reliant on getting favorable matchups to outscore. Both of these factors would impact the shot totals and indicate that simply comparing total shots at home to total shots on the road would in many cases likely not be sufficient to properly assess whether the official scorers were accurately recording shot information.
Next time I will take a look at the expected and actual shot numbers for all teams, and use them to calculate offensive and defensive zone shots-per-minute rates to add some more information to the shot recording picture.
Philip Myrland is an author of Puck Prospectus and runs the statistical hockey website Brodeur Is A Fraud. You can contact him at BrodeurIsAFraud@Inbox.com.
Philip Myrland is an author of Hockey Prospectus.
You can contact Philip by clicking here or click here to see Philip's other articles.