# Just Swing the Bat: Swing Percentages By Inning

With the final pitch of this past world series in the book, we now have two iconic series-ending takes in recent memory. Miguel Cabrera was frozen by a Sergio Romo fastball when he was perhaps thinking slider, and Carlos Beltran famously flinched at an Adam Wainwright curveball in game seven of the 2006 NLCS.

Of course that’s just two data points, connected only tenuously by situation (last out) and outcome (strike three taken), but it is enough to spawn a digression. Even if it would be kind of crazy to find out that batters swing less often as your average game progresses based on this starting point, crazier things have been born of less consequential moments.

With the help of sabermagician Jeff Zimmerman, I set out to answer this question. Seems easy enough. How often do batters swing, by inning? Let’s limit it to at-bats against starters, considering the difference between a starter making his way through the lineup again in the sixth inning and a fresh reliever in the same inning.

[Updated Thursday Night]

Inning Z-swing%
1 58.90%
2 59.80%
3 60.40%
4 63.20%
5 62.70%
6 64.50%
7 64.60%
8 64.10%
9 62.90%

Um. So we’re done here? The “n” in even the smallest bucket is over 1800. And there go the swing percentages, increasing steadily as the game goes on. Easy enough to see. Case closed?

Except that it’s entirely possible that the pitchers are throwing more strikes as the game goes on. Let’s check how often the starters chuck it inside the zone, by inning:

Inning Zone%
1 55.10%
2 55.80%
3 55.30%
4 54.40%
5 54.80%
6 54.00%
7 54.90%
8 55.70%
9 53.50%

Okay so batters are swinging more against starters as the game goes on, but starters are throwing the ball in the zone just a fraction less. That strange blip in the ninth inning of both tables reminds us, though, that there’s a survivor bias in here. A starter that’s still going in the ninth inning is probably having a great game. What happens when we add the relievers back in?

Inning Z-swing% Zone%
7 62.30% 54.10%
8 62.80% 55.00%
9 62.00% 55.60%

Everything goes out the window. If batters were swinging more as the game went on, they checked that tendency at the door when a reliever came in the game. If the starters were chucking it in the zone a little less as the game went on, the relievers came in and started afresh with a zone percentage that looked more like it belonged in the first inning.

If there is an interesting string to follow here in the future, it is the slight chance that starters who remain in the game begin playing some sort of cat-and-mouse game, where they throw the ball in the zone less and the batters swing more at the pitches that are left in the zone. Could there be a general relationship between batters faced, and zone and swing percentages? We’ll keep looking.

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Graphs: Baseball, Roto, Beer, brats (OK, no graphs for that...yet), repeat. Follow him on Twitter @enosarris.

Guest
3 years 8 months ago

I love your study. I love statistics and baseball. I use statistics to help me catch HR’s as a fan.

Guest
Well-Beered Englishman
3 years 8 months ago

This post is a genius observation married to genius data!

Side note: would you say that the relievers’ decline in zone % is coincidental? Or are closers really slightly less likely to throw the ball in the zone than, say, a long man or the starter?

Guest
Dan
3 years 8 months ago

Other possible contributing factors to lower zone rates for starters as the game continues are: 1) reduced command of pitches due to fatigue, and 2) increased reliance on secondary pitches upon facing hitters the second and third times through.

Member
Member
3 years 8 months ago

Why not just look at Z-Swing%? Then you can see how often batters are swinging at strikes as the game progresses without worrying about Zone%.

Guest
dcs
3 years 8 months ago

I don’t understand the data. The Sw% should be around 45% instead of 54%, and the Zone% should be around 50% instead of 75%.

Guest
MGL
3 years 8 months ago

You are seeing all kinds of things happening here. One, you have the times through the order thing, whereby the batters gain an advantage each time they see the same pitcher (the starter). That enables them to swing more at strikes.

The pitchers meanwhile, throw fewer strikes because batters are swinging more, are more familiar with their stuff, they throw more breaking pitches, and perhaps are getting fatigued (that is probably the least of the factors as most starters don’e last long enough to get fatigues these days).

The last inning and to some extent the 8th inning is NOT because starters who are pitching great continue to pitch great. I have done extensive research on this and have found that starters who are pitching great through the 6th or 7th innings, pitch normally (as their seasonal stats would suggest) in the 8th inning, including the times through the order penalty. In other words, a mediocre starter who is throwing a shutout through 7 innings, pitches really lousy in the 8th inning, considering that he is a mediocre pitcher to start with and that he is facing the order for the 3rd or 4th time. Why do managers almost always leave in their mediocre (or bad) starters in the late innings when they don’t have a high pitch count, despite the fact that the data shows that they pitch lousy when left in, even when pitching a great game? Because the wrongly believe that pitching a great game through x innings means that you will continue to pitch well after that AND they are apparently unable to tell from watching the pitcher, talking to him, the catcher and the pitching coach, that there is anything magical about his stuff or his mechanics that day. This is contrary to the beliefs of virtually every player, manager, coach, and fan, right? But it is true. Starters who pitch great through x innings pitch how they normally pitch after that, plus the times through the order penalty. Which means that you should get your mediocre starter out of the game as soon as possible regardless of how he is pitching, not considering bullpen preservation issues of course. The time to preserve your bullpen, though, is when the game is lopsided (low leverage). That is the time to extend your mediocre (or any) starters if you want to preserve your bullpen, regardless of hoe he is pitching. Or you bring in your junk man for extended innings (at least until the game gets close) – the guy who you can send down and bring someone else up. The guy who stinks anyway.

Sorry for the digression – I thought that was important. Anyway, the 9th inning (and to some extent the 8th) is a different animal when it comes to starters (and the batters). Starters tend to be in the game in the 9th with a large lead. Relievers tend to be in the game in the 9th when a team is losing (especially in the NL) or with a large lead, mostly the latter (with a large lead).

What happens when a pitcher pitches with a large in the 9th? He should throw more strikes, at least until the tying or winning run comes to bat. But according to the chart, that inning the lowest zone percentage for starters. I have no idea why. Fatigue? That would start to show up in the 8th but the 8th has the highest zone%. So I have no idea what is going on there, other than the 9th and somewhat the 8th, is a strange inning when starters are still in the game, likely because of specific end-game strategies for pitchers and batters.

You would also expect to see batters taking more pitches in the 9th against the starters since, as I said, that tends to be when the batting team is behind by at least 2 runs. And they do. They swing more often at strikes through the 8th inning, because of the “times through the order” familiarity factor, and then swing a lot less at strikes in the 9th, as you would expect.

Guest
Baltar
3 years 8 months ago

This is the way science works. It’s as important to disprove hypotheses as to prove them.