The Secret Benefit (And Cost) Of Sweeping Sliders

© Kirby Lee-USA TODAY Sports

I, for one, am not a fan of the breakout of the “sweeper” in recent years. It’s not because I don’t enjoy frisbee-ish pitches that seem to pull out a map, ask for directions, and take a sharp turn on their way from the mound to home. A big part of my job is making GIFs of fun pitches, so I obviously love that part. Personally, I just don’t like the annoyance involved in classifying them.

To give you an example, I decided to do some research on sweeping sliders, or whirlies if you’re into weird nomenclature. In fact, that’s what this article is about. On my way to doing so, however, I had to spend some time getting obnoxiously technical. First, I downloaded all the sliders that right-handed pitchers have thrown this year. I separated them by movement profile, then started asking questions.

I asked a few people, “Does this scatter plot look like it separates out sweepers and non-sweepers to you?” It kind of did, and it also kind of didn’t. Are pitches that have 30% more horizontal break than vertical break sweepers? What about 50%? What about pitches that break a foot horizontally but move six inches downward? I sent several variations of that chart trying to nail it down, but nothing felt quite right – I’ll spare you having to look at the mess I ended up with.

The best definition I could find for a sweeper comes from Dan Aucoin, but even then, there are weird bright line issues. Should a pitch that breaks a foot horizontally and 1.75 inches downward be a sweeper, while another that breaks a foot horizontally and 2.01 inches downward be a regular slider? What about its velocity? And what about a pitch that’s a millimeter short of having enough horizontal break? It’s just downright hard to make definitions like this work, a good reminder that pitch classification is extremely difficult when a pitcher isn’t telling you specifically what they’re throwing.

That mini-rant aside, I did eventually end up deciding how to define a sweeper so that I could get on with my research. It’s been a revelation seeing the Dodgers, Rays, and Yankees tap into seam-shifted wake to reinvigorate various pitchers’ careers. Still, I had a sneaking suspicion that as neat as the pitch is, it’s not a panacea. I’ve seen enough games where a righty pitcher floats in a handful of big breakers to his left-handed opposition to wonder how effective sweepers are without the platoon advantage. For every perfectly located back-foot slider, I can call several no-chancers to mind, either crushed for line drives or comfortably taken for balls.

To measure this effect, I split all sliders into two buckets: sweepers and non-sweepers. I further bucketed them by handedness. Here are the physical characteristics of my two groups when thrown by right-handed pitchers against right-handed hitters:

Slider Shapes (Excluding Gravity)
Characteristics MPH HMov (ft) VMov (ft)
Non-Sweeper 85.3 0.43 0.15
Sweeper 82.6 1.17 0.19

And here’s how both types of sliders have performed in those right-right matchups:

Regular and Sweeping Sliders, RHP vs. RHB
Characteristics SwStr% Whiff% GB% PU% BABIP HR/CON Run Value/100
Non-Sweeper 17.0% 35.3% 45.6% 13.1% .277 3.9% -0.26
Sweeper 17.1% 36.4% 33.0% 20.3% .246 4.0% -0.94

Holy mackerel, that’s a low BABIP. If you wonder why the Dodgers are allowing a .258 BABIP this year, their defensive positioning surely helps, but so does the fact that a pitch they popularized turns balls in play into outs at a heady clip. I included popup percentage (which I manually defined as batted balls hit at 45 degrees or higher) because I was reminded of Owen McGrattan’s research into that very phenomenon. Want some outs on balls in play? Get them in the air at a lazy angle. It’s not rocket science, though Los Angeles probably employs plenty of rocket scientists.

If you want a short encapsulation of the sweeper’s advantages, that chart is exactly what you’re looking for. The pitch misses just as many bats as a “regular” slider, and gives up just as many home runs per ball in play. But it gets more soft fly balls and popups, which results in a much lower BABIP and thus much better outcomes for the pitcher.

When you put it that way, it’s no wonder pitchers are trying to throw more sweepers. If your pitching coach came up to you and said “Hey, you have an average slider, let’s turn it into an average sweeper,” why would you say no? It’ll miss just as many bats as your old pitch, and also get better results on contact. If you’d prefer it in wOBACON terms, sweepers allow a .325 wOBA on contact, while “regular” sliders allow a .357 mark. Easy peasy.

How does the sweeper hold up against lefties? Bad news:

Regular and Sweeping Sliders, RHP vs. LHB
Characteristics SwStr% Whiff% GB% PU% BABIP HR/CON RV/100
Non-Sweeper 15.6% 31.8% 38.4% 14.6% .268 5.2% -0.35
Sweeper 12.9% 28.5% 32.8% 16.1% .284 4.4% -0.05

In essence, that contact advantage goes away. Lefties hit more line drives against the pitch, and don’t pop up at the same elevated rate. In wOBA terms, regular and sweeping sliders both allow a .370 wOBA on contact, but sweepers are at a disadvantage when it comes to missing bats. That makes intuitive sense to me. Pitches that break towards a batter are easier for them to see; that’s why pitchers use changeups to fight opposite-handed hitters.

If your sweeping slider doesn’t have an edge on contact, that’s a problem. That’s the whole reason you throw the pitch; if it doesn’t do better on contact, and it’s breaking towards left-handers’ bats, you should really shelve it. Pitchers more or less know this; they halve their sweeper usage to opposite-handed batters.

Maybe that’s not a huge problem, because pitchers halve their overall slider usage when they don’t have the platoon advantage. I’d argue that they don’t need to, at least not as much – bullet sliders demonstrate smaller platoon splits, although not always to the extreme that they have this year. Even though the term “sweeper” has only entered baseball vernacular recently, people still threw them. I used the same criteria to hunt down platoon splits for the two slider variations in the past four years:

Slider Platoon Splits (Run Value/100 Pitches)
Year Regular vL Regular vR Platoon Gap Sweeper vL Sweeper vR Platoon Gap
2019 -0.26 -0.54 0.28 -0.39 -1.59 1.2
2020 -0.32 -0.59 0.27 -0.75 -0.34 -0.41
2021 0.07 -0.19 0.26 -0.3 -1.26 0.96
2022 -0.35 -0.26 -0.09 -0.05 -0.94 0.89

I don’t want to act like this is some unassailable logic, proof that I’ve cracked the mysteries of this pitch variation. There are huge population issues; the pitchers who throw sweepers aren’t the same as the ones who throw regular sliders, at least not in every case. The average pitch quality might be different; the average opposition might be different, too. The sample sizes aren’t even huge; there have already been nearly twice as many sweepers thrown in 2022 as were thrown in 2019, and the season isn’t over.

But even taking that into account, I have some bullet points for you the next time you watch someone throw a big, sideways-breaking slider with a bit of velocity. One: it’s going to get a ton of popups and suppress BABIP, even if it doesn’t miss extra bats. Two: it has a meaningful weakness against opposite-handed pitchers. For what it’s worth, the left-handed pitcher sweeper data looked similar, but the sample was so small that I just discarded it.

What does that mean? First, I think that sinker/slider pitchers should mostly only throw sweeping sliders if they’re relievers. Relievers get the platoon edge far more often, and they also don’t have to see the same batter twice; you can get away with four straight sinkers to a lefty, but probably not eight. If your job is to get righties out, and you can learn to throw a sweeper instead of a tighter slider, that seems like a good tradeoff to me.

Second, if you’re a Yu Darvish-esque pitching savant, capable of throwing anything and everything, the kind of guy who Pitch Com doesn’t work for because it doesn’t have enough buttons, why not add a sweeper? If your arsenal is already so deep against opposite-handed pitchers that you don’t need a slider there, it seems like something worth toying with. That contact suppression looks real; across all four years of data, right/right sweepers have allowed a .248 BABIP.

I don’t think this will continue indefinitely, for the record. It’s still a competitive advantage for some teams, but more teams are teaching it, and there’s a natural cycle to pitches like this: more and more pitchers throw it until too many pitchers throw it, which affects the aggregate quality. Then its popularity wanes, and only the experts are left throwing it. Sinkers went through a similar pattern; I think splitters might be next. Sweepers are neat, and they have a lot working in their favor, but don’t expect them to replace tight, bullet-style sliders overnight.

Ben is a writer at FanGraphs. He can be found on Twitter @_Ben_Clemens.

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4 months ago

The broom of the system