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.