Strikeouts and Leagues and a Historical First

You know who sucks at hitting? Pitchers. Boy, they just really suck. Pretty much always have, probably always will. Sure, every so often, a random pitcher will run into one and blast a dinger out of nowhere. But the same could be said of Munenori Kawasaki (now), and while pitchers aren’t automatic outs, they’re as close as you’re going to get to automatic outs in a regular major-league baseball game. Maybe this calls for a reminder that pitchers only suck relative to big-league position players. They’re better at hitting than us. But their numbers are always deplorable, and we don’t always have to be all fair-like. When a pitcher bats in a rally, you assume that the rally is over.

The designated hitter became a thing in 1973, following various proposals. From that point on, pitchers stopped hitting in the American League, while they continued hitting in the National League. In the previous sentence I have explained the most basic of rules. Thus, NL pitchers faced a lot of pitchers, while AL pitchers didn’t, even after the advent of interleague play. Unsurprisingly, then, since the DH came into existence, NL pitchers have posted a higher strikeout rate than AL pitchers. They’ve posted a higher strikeout rate every single season.

Except for this one, so far. The season isn’t over, and the first half of the season isn’t over, so we can’t draw sweeping conclusions yet. But here I’ll present to you a telling graph:

For 40 years in a row, NL pitchers struck out a higher rate of batters than AL pitchers. There would’ve been a variety of reasons, but mostly, it was about getting to face other pitchers. This year, we find the AL rate to be 20.0%. Meanwhile, in the NL, it’s 19.7%, for a difference of +0.3%. The closest they’ve been before is -0.1%, in 2007. On average, the difference has been about -1.0%. We can’t yet say the AL posted a higher strikeout rate for the first time in the DH era, but the leagues are on that course.

So why might this be? For every curious observation, we ought to look for explanations. This time, there are a few good ones. You’ve probably already thought about them.

Houston Astros factor

When you see a long-term trend change like this, you might first wonder whether there have been changes to the underlying structure or rules. Indeed, the Astros just moved from the NL to the AL, which is a pretty significant adjustment. The Astros have been bad, and they remain bad, and they remain a team that strikes out a whole hell of a lot. In a sense, a single team can mean only so much when you’re talking about a league of 15. But, about the Astros.

This year’s Astros are on course to have the highest team strikeout rate in baseball history. Strikeout rates, of course, have been rising, and it might be better to compare them to the league average, but the Astros are ahead of the 2010 Diamondbacks, and everyone else. Just this year, they’re comfortably ahead of the Braves and the Mets. Maybe things are changing — over the last 30 days, the Astros have been only second-worst — but what’s happened so far is what’s happened so far. The Astros strike out a lot and they just changed their league.

AL pitchers have faced Astros batters more than 2,300 times, while NL pitchers have faced them 500 times. If you just remove the Astros from the equation, the NL strikeout rate stays at 19.7%, but the AL strikeout rate drops to 19.6%. The NL has its own bad teams, but it doesn’t have a bad team this exceptionally strikeout-prone.

Detroit Tigers factor

Speaking of crazy strikeout rates. The Astros are on pace to have the highest team strikeout rate ever, at the plate. The Tigers are on pace to have the highest team strikeout rate ever, on the mound. We find the Tigers at 25.1%, and the historical runner-up is the 2012 Rays, at 23.1%. This year, the Red Sox are in second place at 22.3%. No matter what the Tigers do from here, so far their strikeout numbers have been nothing short of absurd, giving the AL a second exceptional advantage.

As noted before, the AL has a league strikeout rate of 20.0% on the mound. If you were to just drop the Tigers from the equation entirely, then the rate sinks to 19.6%, putting the AL just below the NL. One team can’t make an enormous difference in a league of 15, but one team can make enough of a difference, for these purposes.

Fun fact: the Tigers have played the Astros seven times, going 6-1. In 68 innings, they’ve registered 76 strikeouts, for a rate of 29.6%. Their strikeout rate against non-Astros is 24.7%. Against Tigers pitchers, Astros hitters have batted .189/.238/.290. We’re going off course.

Interleague factor

With the Astros change came a corresponding change in the schedules. Used to be that 20 teams played 18 interleague games, and ten played 15. Now every team plays 20. Last year, AL pitchers faced NL hitters 11.1% of the time, and NL pitchers faced AL hitters 9.8% of the time. So far this year, those rates are 13.6% and 13.8%. AL pitchers post higher strikeout rates in interleague play than NL pitchers, probably owing to slight AL superiority. The AL’s interleague strikeout rate this year is 20.6%. For the NL, it’s 18.7%.

It’s worth noting that AL pitchers are facing a very slightly higher rate of opposing pitchers, while NL pitchers are experiencing the opposite, as a consequence of the interleague scheduling adjustments. As was talked about earlier, pitchers suck at facing pitchers. But this is a very minor factor, relatively speaking. The American League as a whole, as pitchers, has 178 total plate appearances against other pitchers. Last year, the total was 277. Of those plate appearances, nearly two out of five have ended with strikeouts.

Overall

Historically speaking, this has been a weird year, because the AL pitchers aren’t supposed to strike out more batters than the NL pitchers. That’s never happened before during the DH era. But it seems like it’s pretty easily explained, so, at least there’s that. We can’t really say the average AL-pitched game is featuring more strikeouts than the average NL-pitched game, because while that’s true, it’s a little misleading, because it seems to be due mostly to two unusual teams. They exist, and their numbers are their numbers, but it’s not like rates have changed across the board. What does this mean to you? Probably not anything at all, unless you’re a fan of league statistics. But you might be a fan of league statistics.