"Defence wins championships" is a familiar cliche that is thrown around as a truth in not only hockey circles, but by fans of virtually every team sport. At some points in hockey history it may have been true, but I believe the game has changed. In the new NHL, the evidence suggests that offence wins championships.
First of all, I'll give the small sample size warning to everything that I'm about to post. Past results do not guarantee future performance and so on. I tend to believe the numbers show a real effect since regular season results have generally fallen in line, but I'm going to be focusing on playoff results only which means that the sample is limited to 60 playoff series over the last 4 seasons.
Secondly, I'm ignoring all shootouts here. Goals for and goals against mean actual goals, not the goal awarded in the standings to the team that won the shootout. I counted all games that went into a shootout as ties for both teams, so because of that a few times I considered a team that finished lower in the standings to have had a better record than their opponent. This approach makes sense to me since shootouts don't happen in the playoffs.
It is important to realize that in the playoffs nothing happens with a high degree of certainty. Upsets regularly happen in short series. Just to establish a baseline, over the period from 1955-2009 the team with the better regular season winning percentage has won 65% of the playoff series. Since the lockout the percentage has fallen to 61%, which likely reflects the higher level of parity in today's game.
If the better overall team wins 61% of the time, how does the better offensive team do? Answer: The team with more goals scored has actually done even better, winning 37 of the last 60 series (62%). That's a much better success rate than the team with fewer goals allowed, which has won just 27 series (45%).
Often the same team will be better in both categories. For example, the 2008 Detroit Red Wings had better regular season offensive and defensive numbers than all four of their playoff opponents. Let's look only at series when a team with more goals scored plays against a team with fewer goals against, the classic offensive team vs. defensive team scenario. In those matchups, the stronger offensive team has won 24 out of 38 times (63%).
The numbers also show the value of looking at a team's win threshold. The team with the better win threshold won 38 out of 60 series (63%). Win threshold has been a better predictor of success since 2006 than a team's overall record or number of goals scored. As you can infer from that result, a team with a higher win threshold was slightly more likely to win than an opponent with a lower win threshold even when the latter had a better win/loss record, although this advantage was slight (11/21, 52%).
When we focus on goaltending, we also see that the post-lockout playoffs have been determined primarily by the play of skaters, rather than by the play of the masked men. The team with the better regular season save percentage has won just 25 out of 60 series (42%). When a team with a better save percentage has played against a team with a better record, the team with the better goaltending won just 7 out of 25 series.
If you look at each position individually then goalie is the most important position in hockey, but the 18 skaters as a group are collectively much more important than the goalie. A good measure of the effectiveness of the skaters is a team's win threshold. Since the lockout, when a team with a better win threshold went up against a team with a better save percentage, the team with the better skaters won 26 out of 39 times (67%). Given the uncertainty of playoff results in hockey, that is a very high probability.
There is another cliche that goes something like, "In the playoffs you don't need a great goalie, you just need a hot goalie". If you have a dominant team then you might not even need that, but for most teams that is probably not far from the truth. The abundance of good goalies in today's NHL means that a lot of teams have a goalie that is capable of excellent play for a month or two. The best goalies are not able to be the difference makers that they perhaps once were, and that means that goaltending ranks well behind a team's offensive ability in terms of predicting their success.