The Utah Jazz have been playing much better when rested
This year, the Utah Jazz are 3-16 (.158) when they've played the night before, compared to 44-17 (.721) when they had the night off.
That's obviously a huge difference, close to 5 standard deviations. In two articles this week, Carl Bialik suggests that playing better in back-to-back games is a characteristic of a team, and may have predictive value in the playoffs:
"Two years ago, the Dallas Mavericks' 15-1 record in second legs of back-to-back games helped them earn the Western conference's top seed. Conversely, the Golden State Warriors were 5-17 without a day off. When the two teams met in the opening round of the playoffs, Golden State showed they were better than their No. 8 seed by sending the Mavericks home."
But: a quick check over at Basketball Reference shows that there might be a simple reason the Jazz haven't played well in those 19 games -- they're predominantly road games. Only three of the 19 games were at home (although Utah did lose all three).
The home-field advantage in basketball is by far the highest of the four major sports (the home team wins 60.8% of games, according to this presentation (.pdf)). If the average team is only .392 on the road, that works out to 7-12 (actually, close to 7-and-a-half wins). The Jazz still undershot, especially if you consider that they're a better-than-average team -- but not by as much as if you thought they should have been .721.
Basketball is also the sport in which the better team wins most often, and you could probably close the gap even more by accounting for the quality of the Jazz's opposition in those 19 games. I haven't looked, though. And, of course, the Jazz were cherry-picked for the article because of their extreme split -- Bialik says it's the largest in the past five seasons. If you assume the Jazz "should have" been, say, 9-11, then 3-16 doesn't seem that weird for being the worst outlier.
As for the Mavericks in 2006-07 ... they also played most of their second of back-to-back games on the road -- 10 out of 14 (I must have missed a couple from the game logs). Again, you'd have to check the quality of opposition to see if they played particularly weak opponents.
By the way, Bialik says that over the past five seasons, teams win 44% of their played-the-night-before games. That seems unremarkable, considering that it looks like those are predominantly road games.
Finally, I almost forgot about this study on how NBA teams play when rested.