This Is the Postseason of the Home Run

Yesterday was a good day for the Yankees and the Cubs. The Yankees moved to the brink of making the World Series, while the Cubs managed to avoid NLCS elimination. From a less team-oriented perspective, yesterday was also a good day for the home run. In Chicago, Willson Contreras started the scoring with a long solo shot. Javier Baez hit two solo dingers of his own, while the Dodgers got solo shots from Cody Bellinger and Justin Turner. In New York, Gary Sanchez launched a homer out to left. There were six home runs hit, on a day in which there were just 10 total runs scored. For none of the homers were any runners on base, but even so, that means that dingers accounted for 60% of the offense.

Now, 60% is extreme. It should be considered a one-day blip. And yet it does still fit a pattern. So far in the playoffs, we’ve seen a total of 234 runs. Of those, 115 have scored on homers. That means that 119 have scored on non-homers. You’ll notice that 115 and 119 are almost identical.

This was already the year of the home run, in the era of the home-run spike. We’ve gotten used to home runs. Some people are even beginning to find the home run to be boring. Like it or not, it’s here, for now. While the other indicators have trended in favor of the pitchers, hitters have fought back by attacking the stands. This is all background, and it’s a concept you already understood.

Analysts have talked about home-run runs for some time. We’ve long known there to be offenses that are more or less home-run-dependent. It’s thanks to old Baseball Prospectus that there’s a name for this stat: the Guillen Number. The Guillen Number is simply the percent of runs, for a team or for a league, that score on homers. The higher the Guillen Number, the more home-run-dependent the group. Easy enough, so, now, I’ve prepared for you a plot. This covers the wild-card era, stretching back to 1995. You see the league-average Guillen Numbers for the regular season, and I’ve also included a line for the playoffs.

The playoff line is more volatile, because of course it’s more volatile; the samples are much smaller, and not all teams are represented. The average playoff Guillen Number has been 39%. The low is 28%, for 2000. The high is 49%, for 2017. Now, that isn’t the high by far — the Guillen Number was 48% for 1998, and 47% for 1995. There are ups and downs. But you can see how the playoff line might be trying to trend up. Three years in a row, now, more than 40% of all postseason scoring has come from the homer. That makes sense in large part because, if you look at the regular-season line, we’re experiencing a spike. The league just had a Guillen Number of 43%. The average for the whole sample is 36%. It never got as high as 40% until last year. More and more offense is coming from the homer, which, well, you knew that, probably. But it’s the only thing currently propping up run production.

So, one more time, homers this month have accounted for nearly half of the runs. That’s a greater dependency than usual, and I think it can be further understood by studying the following plot. One of these lines shows simple playoff OPS. The other one shows playoff OPS if you remove all home runs from the numerator and denominator.

The red line was always going to be a great deal lower than the blue one, because home runs are vitally important. But if you look at the overall OPS line, this year is at .698, while the wild-card-era average is .705. Pretty close. If you look at the line that eliminates homers, this year is at .528, while the wild-card-era average is .570. Last year’s playoffs finished at .524. The year before that, .509. There’s going to be noise, here, but this is also reflecting known trends and realities. Playoff defenses are better. Playoff pitching is better, and getting better still. The current playoff strikeout rate is up past 25%. Offenses need home runs, because it’s incredibly difficult to score via other means.

With home runs excluded, the current playoff batting average is .192, which is the lowest in the sample. With home runs excluded, the current playoff slugging percentage is .245, which is the second-lowest in the sample, missing the top position by one point. It’s been said before that the playoffs make it very hard to string together hits and walks. It’s only getting tougher, as playoff pitching improves, and managers more aggressively go to their bullpens. You can still score by linking together consecutive at-bats, and some teams might squeeze out extra productivity by getting aggressive on the bases, but there’s nothing quite like a playoff home run. Every run as at a premium, and a homer can happen in the blink of an eye.

There is one potential counterpoint — maybe playoff lineups are growing too homer-dependent. Maybe they’re not giving themselves enough of a chance, and maybe they could make more contact if they wanted to. Maybe they could walk more if they wanted to. Maybe they could steal more if they wanted to. Maybe, in the playoffs, teams decided they need to hit more homers, so they focus on trying to hit more homers, and that influences the overall stats. But it’s not clear that anything is failing. Right now, overall playoff OPS is basically right where it’s been for a couple of decades. It’s not that there aren’t any runs. It’s that there are precious few of the non-homer runs. Nearly half of the runs have scored on a dinger. That’s the game we have today, and it means the whole complexion can change with any swing.