Why the Front-Door Sinker Isn’t a Trend… Yet

It may be impossible to believe after the last two games — after all the front-door sinkers thrown by Corey Kluber that turned the Cubs’ bats into mush and after a similar experience last night facilitated by his apprentice Trevor Bauer — but the front-door sinker is not a hot new trend in baseball.

First, to review: the front-door sinker is thrown from a pitcher of one hand to a hitter of the opposite one. The intention? Essentially, to fake the batter into not swinging. It’s a sinker thrown at the hip that then moves into the strike zone. Here’s an example from August Fagerstrom’s piece on Kluber this week:

Seems like a rad pitch. In the era of the swinging strike, it’s a pitch that’s designed to elicit a take. It relies on command in an era when we wonder if pitchers even have any command. After all, as I noted in my for last year’s Hardball Times Annual, the average pitcher misses the catcher’s target by more than 11 inches on a 3-0 count.

Miss the spot on a front-door sinker by 11 inches and you’re either hitting the batter or drifting into the middle-outer third of the strike zone, where many lefty swings go to eat. Maybe that’s why it looks like there isn’t any real trend in front-door sinker usage over the PITCHf/x era, even as the inside part of the lefty strike zone is expanding, according to Jon Roegele’s research.

Look at where sinkers have been thrown from righties to lefties in three-year increments over time, and there’s virtually no difference.

You’ll see that the sinkers are being located a little lower in the zone, but that’s a league-wide trend due to the expansion of the strike zone at the bottom. Generally speaking, however, pitchers aren’t really throwing more sinkers inside to lefties. Those buckets in both windows hover from 300 to 500 sinkers, which is a decent amount, but not when put against all the other buckets.

Jonah Pemstein ran a query looking for all two-seamers that were thrown off the plate but whose movement brought them back over it, which is a more complete way of asking the question. It includes both front- and back-door sinkers, but the mechanism is the same: the pitcher throws a fastball that looks like a ball, elicits a take, and then comes back over the plate for a strike.

There may have been a mini trend at one point, but it’s now gone.

Front & Back Door Sinkers Over Time
Year Front/Back Door Sinkers wOBABIP Called Strike%
2010 14352 0.354 41.4%
2011 15876 0.387 39.9%
2012 18250 0.397 37.5%
2013 18327 0.392 35.7%
2014 18782 0.385 35.4%
2015 17149 0.387 36.0%
2016 16739 0.417 36.2%
wOBABIP is the weighted on base average on the balls put in play

There was a time that pitchers threw this pitch more often, and then they stepped away from it. The clue to why comes in the two rightmost columns. For one, if you miss your spot just by a few inches, and the hitter swings, and puts the ball in play, he’s about to get happy. The league weighted on base average around this time has hovered around .320. Batters love to swing at fastballs in the zone, and this is a fastball in the zone.

We had an example of this last night. Bauer executed his front-door sinker to Anthony Rizzo well! The pitch nicked the inside of the zone, and the book on Rizzo is to throw him inside. The problem was that Kluber threw that pitch to Rizzo the day before, too — and, this time, instead of taking it for a called strike, Rizzo swung.

The last column in the table above might be just as difficult to the prospective back-door-sinker thrower. Remember, the query run by Pemstein sought to identify which pitches featured sufficient movement to move them back into the strike zone. So that last column should be littered with figures in the 80% range, since the average efficacy of an umpire on most pitches is around 85%. They don’t see front-door sinkers that well.

We know why. The strike zone is theoretically a three-dimensional box, one that extends backwards as it heads towards the catcher. But our technology so far has focused on the front of the strike zone as a two-dimensional plane, a plate of glass. That’s trained our umpires to look at where the ball is when it crosses the front of the plate. Umpires are not good at breaking balls that hit the side of the plate, which basically what front-door sinkers do. Robots will call these pitches much more often.

That’s for later. If you like the front-door sinker, you should be a fan of the robot umpire or the expanding strike zone to lefties inside. Now? It’s a little dicey to throw that thing and risk a swing on a middle-middle fastball, especially if you’re only going to get a call on a strike 40% of the time. Just another reason we know that Kluber is a robot: he fears none of this.

With a phone full of pictures of pitchers' fingers, strange beers, and his two toddler sons, Eno Sarris can be found at the ballpark or a brewery most days. Read him here, writing about the A's or Giants at The Athletic, or about beer at October. Follow him on Twitter @enosarris if you can handle the sandwiches and inanity.

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7 years ago

“Generally peaking” <- think you dropped an S there