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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