Last night we almost saw two amazing comebacks in the NBA playoffs:

• In Indiana, the Pacers were down by as many as 30 points to the Hawks in the third quarter before a furious rally cut the deficit to nine points with 1:54 remaining. That was as close as the Pacers would get, though, and they eventually lost by 10 points.
• In Dallas, the Spurs led the Mavericks by 20 points in the third quarter but saw that lead dwindle to just one point with 0:19 remaining. San Antonio held on, though, for a four-point victory.

Those games got me thinking: What was the greatest comeback in NBA playoff history?

I don’t have play-by-play data earlier than the 2001 playoffs, so I can’t necessarily find the largest deficit a team has overcome in a given game.

However, I do have scoring by quarter for almost every game in NBA history, so I used data from the 1980 playoffs — the first year the 3-point shot was used — through the 2013 playoffs to build models to predict the home team’s win probability after each of the first three quarters. Here are the results:

The logit (“z”) can then be used to estimate the home team win’s probability:

p = 1 / (1 + e^-z)

For example, last night the Pacers trailed the Hawks by 20 points after three quarters. Thus their estimated win probability was:

p = 1 / (1 + e^{-(0.3297903 + 0.2131430 × -20)}) = 0.0192

Which, of course, makes Atlanta’s win probability:

1 – 0.0192 = 0.9808

Using this method, here are the ten biggest playoff comebacks from 1980 to the present:

As you can see, just two years ago the Clippers had the greatest playoff comeback of the 3-point era, rallying from a 21-point deficit after three quarters to defeat the Grizzlies.

While I was at it, I decided I might as well build models for the era beginning with the introduction of the shot clock (1955) and ending with the last season before the 3-point shot (1979). Here are those results:

And here are the ten greatest comebacks of that era:

Not surprisingly, comebacks from extreme deficits were less common before the introduction of the 3-point shot.

Looking at the raw data, from 1955 through 1979 there were 21 cases out of 857 playoff games (2.45 percent) where a team overcame a double-digit deficit to win the game, but from 1980 through 2013 there were 84 such cases out of 2,477 playoff games (3.39 percent).

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Let me end this post by returning to my original question: What was the greatest comeback in NBA playoff history?

Given the results above, I would have to chose the Clippers incredible 21-point comeback on the road against the Grizzlies.

I have the play-by-play for that game, and amazingly the Grizzlies held a 24-point lead with less than 8:00 remaining in the game. From that point forward, though, the Clippers outscored the Grizzlies 28-3. That run included a brilliant stretch of shooting by Nick Young, as he nailed three 3-pointers in a 1:00 span to trim a 12-point deficit to just three points.