Is the Yankees’ second-half slide historic?

If you’ve been paying attention to the Yankees in the second half, you know that they’ve been a little underwhelming. After posting a .653 winning percentage in the first three months of the season, the team’s managed just a 31-25 record since. That’s still a .554 winning percentage, and good for a 90-win pace over a full year, but when the Red Sox are close to 110 wins and the Rays are closing on 90, it’s certainly a letdown.

Is this historical, though? Good teams often slow down to an extent in the second half. Nobody is immune to regression, as it’s just too hard to play at a 100+ win pace for most teams. Players get hurt, fall into slumps, and the competition tends to regress to the mean (positively) as well. It takes an extraordinary amount of talent and even more luck to be regression-free for a full season. For proof, look at the Red Sox, seven wins better than their Pythagorean record.

To answer the question of whether this is a historically underwhelming second half, I pulled the winning percentages in the second half for all seasons since 1996, through Wednesday’s win over the Red Sox:

So this isn’t a great second half, but it’s far from the worst. Where the Yankees open themselves up to more criticism is in comparing the first to the second half, by looking at their second half win totals as a percentage of total wins:

By this count, this IS a historically disappointing second half. The number of wins in the second half, when compared to the running total of wins all season, is the lowest in our data set, and it’s not super close. The season isn’t over yet, and this can turn around in a fairly short time since another five or six wins in an 80 game sample can have a big effect. But if you’re wondering why the Yankees are on a 100-win pace after being on a 106-win pace in July, this is why. The second half has just been underwhelming in a relative sense.

What does this mean from a predictive standpoint? Does a letdown in the second half mean the team is doomed to disappoint in the playoffs? The research doesn’t bear that out, whether you ask Ben Lindbergh, Chris Bahr, or Jay Jaffe. And if you’re more into total primary research, take a look here.

The playoffs are just too small a sample size for the “best” team to consistently show itself. It’s also too unpredictable for even the “hottest” teams, which is the real prevailing cliché. For every 2007 Rockies, who roared all the way from a 14-1 finish to the season to a one-game playoff, NLDS and NLCS sweeps, there is a 2017 Cleveland season, where 22 straight wins culminated in an ALDS collapse.

The best team doesn’t always win in the playoffs, and the hottest doesn’t either. The randomness is exasperated by the introduction of a one-game Wild Card playoff, which is the fate the Yankees are destined for. The Yankees haven’t been great in the second half, but it might not matter in the playoff picture, and everything is going to come down to October 3rd anyway, where all previous performance, barring injuries, goes out the window.

Once you’re in the dance, nothing you’ve done up to that point matters. After all: