Friday, May 15, 2015

Heavy Favorites Usually Don't Surrender Big Leads (usually)

The Houston Rockets pulled off the second most improbable comeback of this year's playoffs last night. Down by 19 with 2 minutes left in the third, the Rockets finished the game on a ridiculous 49-18 run to force a game seven in their conference semifinals series with the Clippers.

From 2000 to 2012, there were 624 games in which a team trailed by 19 with 2 minutes left in the third. In just 12 of those games (1.9%) did the trailing team go on to win. But that includes all games, including those in which a heavily favored team fights back from a steep deficit.

The Rockets were 8.5 point underdogs against the Clippers, and heavy underdogs rarely pull off what Houston did last night. Here is the raw data from the 2000-2012 NBA seasons (the raw data behind my win probability model).

two minutes left in the third:
all games 7.5 to 12 pt underdogs
trailing by games won pct games won pct
21 500 5 1.0% 178 0 0.0%
20 599 10 1.7% 203 1 0.5%
19 624 12 1.9% 193 0 0.0%
18 749 17 2.3% 212 3 1.4%
17 843 26 3.1% 242 2 0.8%

Out of 193 games, not a single underdog of 7.5 to 12 points came back from a 19 point deficit. These raw numbers are fairly consistent with the two win probability graphs for this game (by design):

  • The "50/50" version which ignores team strength differences. The Rockets low point was 2.3% in that version.
  • The "pre game" version which factors in the Vegas point spread, with a low point of 0.7% for the Rockets.

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