The slider is baseball’s hardest pitch to hit — at least when it comes from a guy like Sergio Santos.

This season, the 28-year-old White Sox reliever has used his slide piece to rack up nearly 13 strikeouts per nine innings. And consider this: For every 100 sliders Santos throws, he racks up 34 swings and misses — the best in the major leagues for any pitch thrown at least 250 times. That’s also more than double the average rate for sliders. Even more incredible, out of every 100 swings against his sliders, batters miss 63 times — also the highest rate in baseball. That’s simply absurd.

And pretty nasty.



Consider the following:

This graph indicates whiff rate by vertical pitch location, with the blue line representing Santos’ slider and the red line representing the average right-handed slider. The gray bands indicate confidence, and the horizontal bars are approximations of the vertical borders of the strike zone.

It’s not that Santos’ slider is unique in terms of where it gets whiffs. As you can see in the graph, both Santos’ slider and the average slider have their peak whiff rates in the same location — about half a foot below the bottom edge of the strike zone. Santos’ peak is just much, much higher — about 65% compared with 25%.

Perhaps more impressive is his ability to get batters to chase his slider below the zone:

For the average right-handed slider, we find peak swing rates in the lower-middle portion of the zone, which is unsurprising. But with Santos’ slider, batters swing most often when the pitch is at or below the bottom of the strike zone — an area conducive to whiffs. From this, we can infer that deception is a principal reason for his slider’s success.

Santos is very adept at getting batters to chase sliders below the strike zone, where the chance of making contact is extremely low. But while having good velocity and movement can make a slider hard to hit, a pitcher first needs to get the batter to swing at the pitch. Being ahead in the count can force the batter to swing at sliders to protect the zone, but having the pitch look like a fastball is essential. We know that Santos’ slider is disguised well because of the location of swings against the pitch.

When batters swing at Santos’ sliders below the zone — which they do quite often — they don’t make contact. The contact rate against his sliders below 1.5 feet above the ground — an approximation of the bottom of the called strike zone — approaches 10%. For context, the average contact rate is 32% for sliders from right-handed pitchers in the same zone. This underscores the importance of getting batters to chase pitches below the zone, and by extension, deception. While we know that quantifiable attributes like velocity and movement matter, it’s important to keep in mind that qualitative attributes like deception play an important role too, even if we don’t exactly know how important they are.

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