Percentages

There are two ways to win hockey games. Option A is outshooting the other team and winning through a greater volume of scoring chances. Option B is playing even or getting outshot and relying on superior percentages to end up ahead on the scoreboard.

In the long run, teams that outshoot generally have a better chance to achieve success. Over the course of a single season, however, it can be the team that rides a hot streak in terms of percentages that ends up on top of the standings.

The problem with outshooting numbers are that they are often skewed by the score (see JLikens' preview of the Colorado Avalanche for a more detailed explanation of how the score affects shot results). This effect is especially large in the third period, where teams like Colorado and Toronto had strong outshooting results because most of the time they were losing the hockey game. On the flip side, top teams like Detroit and San Jose noticeably shut it down in the third period, trading off some of their outshooting advantage to lower the overall number of scoring chances and increase the likelihood of preserving their lead.

To avoid being misled by the score effects, it is likely better for predictive purposes to look at the data set from the first and second periods only. Using the data from the Hockey Summary Project, I separated out each team's performance in the first and second periods only over the last two seasons. The teams are ranked in order of the projected number of points they could be expected to put up if they record the same shot for/against ratio, shooting percentage and save percentage in the first two periods in 2009-10.

Rank	Team	Proj Pts	SF/SA	Sh%	Sv%
1.	Detroit	113	1.42	8.8%	.902
2.	San Jose	109	1.26	8.8%	.910
3.	Boston	104	0.97	9.6%	.920
4.	Montreal	103	0.91	10.6%	.916
5.	New Jersey	102	1.09	8.4%	.920
6.	Chicago	100	1.05	9.7%	.909
7.	Pittsburgh	99	0.93	10.3%	.914
7.	Dallas	99	1.04	10.1%	.905
9.	Washington	97	1.14	9.0%	.904
10.	Minnesota	96	0.88	9.7%	.920
10.	Florida	96	0.91	8.5%	.928
10.	Buffalo	96	1.04	9.3%	.909
13.	N.Y. Rangers	94	1.14	7.6%	.916
14.	Vancouver	92	0.96	9.4%	.912
15.	Ottawa	91	0.98	9.5%	.908
16.	Philadelphia	90	0.89	9.9%	.912
16.	Carolina	90	1.10	8.6%	.905
18.	Anaheim	89	0.98	9.0%	.911
19.	St. Louis	88	0.97	9.2%	.908
20.	Calgary	87	1.01	9.3%	.903
21.	Edmonton	83	0.82	10.3%	.909
22.	Phoenix	82	0.93	8.5%	.914
22.	Colorado	82	1.03	8.7%	.901
24.	Columbus	81	1.10	7.7%	.906
24.	Tampa Bay	81	0.96	9.1%	.904
26.	Nashville	77	0.97	8.3%	.907
27.	Los Angeles	75	0.97	8.6%	.901
28.	Toronto	73	1.05	8.5%	.891
29.	N.Y. Islanders	72	0.94	7.7%	.911
30.	Atlanta	67	0.79	9.5%	.903

These numbers are not meant to be exact predictions, just historical data. Many teams have turned over much of their rosters and/or coaching staffs since 2007-08, which may mean that some of the numbers aren't very useful for assessing the 2009-10 squads. However, the SF/SA ratio should still have some value in predicting results. The correlation between SF/SA over the first two periods in 2007-08 compared to 2008-09 was 0.79. If a team is returning most of its key players and has the same coach or a similar coaching philosophy there is good reason to expect a similar SF/SA in 2009-10.

The numbers for Detroit and San Jose show the advantage of majorly outshooting the opposition. Detroit demonstrated last year during Chris Osgood's early-season struggles that they could win despite weak goaltending. As long as the Red Wings and Sharks continue to pepper opposing goalies with shots they will win games even with mediocre percentages. In contrast, Edmonton and Atlanta will have almost no chance of making the playoffs unless they drastically improve their territorial play, because it is very hard to compensate for the handicap of facing 20% more shots against.

This chart allows us to see the teams that are relying on percentages rather than outshooting for their success. These teams are more likely to be susceptible to large swings in the standings depending on the luck of their shooters/goaltenders. For example, Montreal's fall from Conference Champs in 2008 to 8th seed in the 2009 playoffs was almost entirely driven by percentages (while Boston's ascent was also pretty much the same story, in reverse). Along with the Habs, Pittsburgh, Minnesota, Florida and Philadelphia are the teams that have been most dependent on having the percentages in their favour.

I'd expect Pittsburgh to be a better outshooting team this year, based on the way they performed late in the season and in the playoffs under Dan Bylsma. If they are they should finish at or near the top of the Eastern Conference.

Philadelphia could also see their outshooting numbers rise in 2009-10 because of additions and the continued maturation of some of their young stars, although I expect a drop in team save percentage might very well wipe out some of those gains. The Flyers are a popular pick among many pundits heading into this season, but I'm not sure they are an elite team yet. However, these numbers might also be selling Philadelphia a bit short, given that they are for the first two periods only and the Flyers were a strong third period team over the last two seasons.

On the other hand, there are several teams that have been outshooting the opposition but have not had as much luck with the percentages. These teams include the New York Rangers, Carolina, Columbus, and Toronto. We saw with both Carolina and Columbus in the second half of 2008-09 what happens when an outshooting team goes from poor percentages to good percentages. The improved goaltending of Cam Ward and better Blue Jacket shooting took both teams into the playoffs. If Columbus continues to improve their scoring ability they could move into the second tier of good teams in the Western Conference, behind Detroit and San Jose.

The Toronto Maple Leafs are an interesting team, since goaltending was the glaring problem that played a big role in sinking their last two seasons. The Leafs were .010 behind every other team in save percentage, which naturally meant they usually were playing from behind. League average goaltending this season probably makes Toronto a playoff contender. It appears the hopes of Leaf fans are riding on the shoulders of Vesa Toskala, or, perhaps more likely, Swedish rookie Jonas Gustavsson.

The other team that was held back by goaltending in 2008-09 was the Dallas Stars. Marty Turco is past his prime but he is still likely to be better this season, and the Stars should be back in the playoff picture.

The Buffalo Sabres have looked like a playoff team in terms of their underlying numbers for the past two seasons. They are slightly above average in all three of shot ratio, shooting percentage and save percentage. Unless somebody has a better explanation I'm inclined to attribute their lack of playoff qualification to bad luck, and the Sabres should have a good shot at returning to the postseason.

I'd say that Edmonton, Phoenix and Colorado are unlikely to make the playoffs in the West. In the East it should be safe to write off the Islanders, and Atlanta is facing a steep uphill climb unless they get some major improvement from their young players. Other than that the picture looks pretty wide open. The elite teams should end up at the top of their respective conferences again (Detroit, San Jose, Chicago, Pittsburgh, Washington), but percentages will play a big role in determining which of the rest of the teams get a chance to play for the Cup.