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May 16, 2009
Rest or Rust
Quantifying the Value of Time Off

by Kevin Pelton

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When the Boston Celtics and the Orlando Magic meet tonight at TD Banknorth Garden for the deciding Game Seven of their playoff series, the most interested neutral observers will be in Cleveland. That's where the Cavaliers are resting and awaiting their opponent in the Eastern Conference Finals. Having gone undefeated through the first two rounds of the postseason, Cleveland has played the minimum eight games thus far. Meanwhile, Orlando will be playing its 13th game, the Celtics their 14th having gone the distance in consecutive series.

If that sounds like an enormous difference in terms of rest, that's because it is. Previously this decade, no conference final series has featured two team with a difference of more than three total games played over the first two rounds.

While this is an extreme example, there's no consensus that the extra rest is a good thing. When the better-rested team struggles in Game One, we're liable to hear about how problematic rust can be in these situations. To get an idea of whether rest helps or hurts over the course of the series, and to what extent, I studied data from the last nine postseasons, 2000 through 2008.

On the simplest level, the team that was coming off the shorter series in the previous round went 23-21 (.523). The surprising fact about these series is that more often than not (23 out of 44 times), the better-rested team was actually the lower-seeded one in the following series. Still, many of those differences were just a single game, and nobody anticipated the L.A. Lakers having a big edge against Houston because their first-round series went just five games instead of six.

A better way to study the issue is to compare a baseline expectation for the outcome of the series based on the teams' regular-season point differentials and home-court advantage to how they actually played out. We can then compare how those series differed from expectations to the rest advantages. Doing this shows rest as having some value, but not much; a regression analysis cannot conclusively determine that there is a positive value to having played fewer games the previous round, and suggests that each additional game of rest is worth about 0.2 wins during the following series.

Looking strictly at previous conference final series limits the sample size, but provides a more relevant comparison as well as the chance to use total games played over the previous two rounds, the criteria we're really interested in considering. Running the same regression shows total rest to be twice as valuable in the conference finals--each fewer game played the previous two rounds is worth about 0.4 wins, meaning a three-game rest difference between two teams could be enough to shift the outcome of one game in the series.

That sounds great for the Cavaliers, who would stand to benefit by nearly two wins using the same logic. However, there's an additional factor that serves to offer hope to fans of the Celtics and Magic--the value almost all seems to go to lower-seeded teams who have the rest advantage. Favorites who have played fewer games over the first two rounds have done basically as well as we would expect in the conference finals. In fact, the last team to sweep the first two rounds of the playoffs (the 2005 Miami Heat) ended up losing at the doorstep of the NBA Finals. On the other hand, underdogs with the rest advantage are an improbable 5-3 in the conference finals.

LARGEST REST DIFFERENCES

Year  Favorite (G)          Underdog (G)         Diff    Winner

2005  Miami (8)             Detroit (11)          +3     Detroit, 4-3
2006  Dallas (11)           Phoenix (14)          +3     Dallas, 4-2
2004  Indiana (10)          Detroit (12)          +2     Detroit, 4-2
2003  San Antonio (12)      Dallas (14)           +2     San Antonio, 4-2
2008  L.A. Lakers (10)      San Antonio (12)      +2     L.A. Lakers, 4-1

2003  Detroit (13)          New Jersey (10)       -3     New Jersey,4-0
2008  Boston (14)           Detroit (11)          -3     Boston, 4-2
2001  San Antonio (9)       L.A. Lakers (7)       -2     L.A. Lakers, 4-0

This makes some sense intuitively. After all, when an elite team plays well in the first two rounds, it's no surprise. Cleveland faced two lesser opponents, and a pair of sweeps were no huge surprise. When a top seed struggles to get to the conference finals, it may be a signal of problems that will prove fatal against superior competition. Alternatively, a lower seed making quick work of opponents may be playing above its regular-season level, like the 2001 L.A. Lakers, who went 7-0 en route to the conference finals and then swept No. 1 seed San Antonio.

By that logic, last night's more interesting result in terms of rest came in the Western Conference, where the Rockets beat the Lakers 95-80 to force their series the distance as well. Should the Lakers win Game Seven, it will be the underdog Denver Nuggets who take the rest advantage into their series and who come in having played better basketball over the first two rounds. History suggests that advantage greatly enhances the Nuggets' chances of pulling off the upset if that matchup comes to fruition.

Kevin Pelton is an author of Basketball Prospectus. You can contact Kevin by clicking here or click here to see Kevin's other articles.

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