Can strikeouts predict how far a team goes in the MLB playoffs?

Introduction

Like all the cool kids these days, I was reading The Athletic the other day. (It’s seriously good, folks.) I came across an article written by Dale Murphy — yes, that one — in which he detailed four things he felt would help a team go far in the playoffs.

One of these four things was strikeouts. As we all know, strikeouts are a big deal these days: pitchers love to get ‘em, hitters seem not to mind ‘em too much. Murphy notes:

Home runs don’t always carry over to the postseason. Power numbers that are accumulated over 162 sometimes might not translate to a five- or seven-game series.

But one thing that does carry over? Pitcher strikeouts.

That got me wondering...

Research Question

Is there a correlation between strikeouts and how far a team advances in the playoffs?

Methodology

Because it takes two to whiff, I thought I’d examine a team’s strikeouts by its pitchers, as well as a team’s strikeouts by its hitters.

I went to Baseball Reference, the Swiss Army Knife of baseball statistics, for the data. I took every season from 2017 back to 2001, because that’s how far I felt like going back, and I figured 17 seasons would be a decent-enough sample. I then looked at all playoff teams in those seasons, and how they ranked in their league in terms of strikeouts by that team’s hitters, and then by their team’s pitchers.

(The AL and NL have each had 15 teams from 2012 onwards, which is when Wild Cards per league increased from one to two, giving us the one-and-done Wild Card game. Before that there was one Wild Card team per league; also, the AL had 14 teams and the NL had 16 teams.)

Because pitchers strikeouts are good, I ranked the top pitcher-strikeout-getting team 1, and the bottom 15 (or 14/16 before 2010); this is “pitching rank.” Because hitter strikeouts are bad, I ranked the team that had its hitters strike out the least 1, and the most 15 (or 14/16); this is “hitting rank (inverse).”

(I recognize these are counting stats, which include extra innings and game 163s, and don’t account for the fact that sometimes a team will only play 161 games in a season due to a rainout not being made up. You’re more than welcome to redo this and take those into account, but I don’t think the effect would be noticeable.)

I also created a “K index,” which is admittedly somewhat hamfisted: I just added together the pitching and (inverse) hitting ranks to get a number I thought might be somewhat useful and interesting. I’ll let you decide.

Data

After the numbers had been typed and the formulas had been formulated, here’s what I got. Remember, lower numbers mean a better rank in their league during the regular season. (There have only been six seasons with two Wild Cards, hence the low n for WC losers.)

Analysis

Since graphs are lovely, I made some.

This is that “K index” thing, which mashes-together hitter and pitcher strikeouts. Generally speaking, the farther you get in the playoffs, the more strikeouts your pitchers got and the fewer strikeouts your hitters got. Interesting little blip with the teams that lose in the LCS and those who lose in the World Series; there’s an old trope around baseball, “There’s more pressure getting to the World Series than there is to win it.” Maybe this is how it comes out; discuss in the comments below if you like.

I think the more interesting graph is the one below, which teases-out the differences between what your pitchers did and what your hitters did.

As with the “index” above, generally speaking, the farther you go in the playoffs, the better you ranked in the regular season (with that odd LCS blip). But, look at the changes in hitting rank and pitching rank: pitching generally strikes out more as the playoffs go on, but the last three categories are basically a wash.

Hitting strikeouts make a much bigger difference: there’s a pronounced gap between World Series winner and World Series loser, in terms of how much their hitters struck out in the regular season. The winners averaged 5.12th in their league, and the losers averaged 7.18th, if I may use those awkward ordinals; that’s two whole spots higher.

Conclusion

Mr. Murphy was generally correct in his statement that pitching strikeouts are a decent predictor of how far a team goes in the playoffs. Hitting strikeouts, however, seem to have a bigger effect, and especially at the end.

Further Research

If someone wanted to do this kind of analysis on home run rank (perhaps only for hitters), it might be interesting to see if the other part of Murphy’s assertion — that power doesn’t translate through to the post-season — is also true.