In the course of predicting all 1,230 games of the 2013-14 NHL season, one common occurrence made me doubt my model more than any other: back-to-back games. My model did a decent job overall when it came to picking games, but I often wondered whether I should have factored the effects of travel and fatigue into my predictions. Home ice provides a consistent advantage in NHL hockey, and is probably the most reliable predictor in single games, but it stands to reason that its effects should differ depending on whether one or both teams enters the game having played and traveled the night before. Yet it doesn’t seem that anyone has done a comprehensive study of the issue before. So, I pulled game dates for all regular-season contests since the 2005 lockout; after excluding season openers, this left me with a sample of 10,403 games. After playing with date functions in Excel, I was able to identify all the back-to-backs and travel in each team’s schedule.
First, I wanted to get a sense of the frequency of back-to-backs in a given season. The table below provides the median number of back-to-backs for each team in the eight 82-game seasons since 2005-06 (2012-13 data, obviously, are excluded). On average, a team can expect to play back-to-backs about 15 times each season, though there are clearly differences among teams. Part of this is likely due to the efforts of league schedulers to minimize back-to-back play for teams that travel more. As such, high-travel teams like Calgary, Colorado, Dallas, Edmonton, and Vancouver average fewer back-to-backs than teams like Buffalo, New Jersey, or the Islanders. In some cases, though, this explanation doesn’t really account for the patterns we see. The Rangers, for example, don’t suffer much at the hands of the schedule-makers, averaging the same number of back-to-backs as San Jose (the team with the most consistently brutal travel itinerary in the NHL) and fewer per season than the Anaheim Ducks, who regularly travel nearly 50,000 miles over 82 games. And the Blackhawks and Blues seem to play a lot of back-to-backs for teams that are regularly around 40,000 travel miles a season.
The real question, of course, is how bad it is to play more back-to-backs than other teams. Or, phrased differently, how does back-to-back play affect the expected advantage of the home team? The numbers based on the 10,000+ games in my sample are depicted below.
Overall, NHL teams playing on home ice can be expected to win about 55.1% of the time. If both teams are playing the second of back-to-back games, the home team’s advantage jumps a percentage point to 56.1%. If both teams are playing the second of a back-to-back after having traveled the night before, as in a home-and-home situation, the home team’s advantage is even greater, at 57.1%. This would suggest that the fatigue effect matters more for the road team, and a look at the more typical scenarios only reinforces this. When the home team is playing a back-to-back against a rested opponent, their win probability drops down to 53.8%, or about 1.3%; if the home side has played and traveled the prior night, their chance of winning drops even further, to 52.8% (down 2.3% from the average). When the visitors are playing their second game in two nights, though, the home team’s win probability goes up to 57.9%, or 2.8% above the average, if they’re rested.
I’ve also presented some comparisons involving relative days’ rest, which are not limited to back-to-backs; the picture here is slightly less clear. A home team with an additional day of rest has a 57% win probability; if they have 2 additional days of rest, they have a 58.7% chance of winning. When playing a road team with 1 more day of rest, their win probability goes down to 53.2%. However, the home side still has a 55.3% win probability when playing a road team with 2 additional days’ rest, and their win probability is actually below-average (53.1%) when they have three or more days of rest. A road team with three or more additional rest days than the home side has the best chance of winning than in any other scenario (47.8%). The sample sizes in the bottom three rows of the table are a good deal smaller than those involved in the other analyses, so it’s possible that these estimates aren’t reliable. There may be some reason why we see these results (maybe road teams benefit more from long layoffs than home teams?), but I’d have to be convinced that there’s something more than a small-samples artifact at work.
To summarize, it looks like having an easier NHL travel schedule carries a significant downside of having to play more back-to-back games (unless you’re the Rangers, in which case you apparently don’t have to worry about either issue). Insofar as the most common scenario in a back-to-back involves a rested home squad, this may explain another piece of the consistent edge that home teams enjoy in the NHL. And more to the point, it looks as though having more back-to-backs might actually be worse than traveling more. Many teams that logged over 42,000 road miles this past season, like Boston, Anaheim, Colorado, San Jose, and Los Angeles, didn’t seem to suffer much from it, and you have to go all the way back to 2009-10 to find a President’s Trophy winner with an easy travel schedule. And though it stands to reason that teams with heavier travel may have longer road trips, it’s not clear that the relative fatigue has a consistent effect on win probabilities. But back-to-back games are pretty much a bad proposition no matter how you look at them, especially if you play them on the road.