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Does Alex Reyes Have the Best Slider in Baseball?

The pitch has elite movement in both directions and was one of the most effective offerings in baseball last season.

MLB: St. Louis Cardinals at Pittsburgh Pirates Charles LeClaire-USA TODAY Sports

Earlier in the offseason, I wrote about Alex Reyes’ breaking balls. At the time, I argued that he should throw more curveballs on account of the pitch having elite movement and a much slower velocity than the rest of his arsenal. I also briefly discussed Reyes’ slider.

To recap, the pitch was one of the most effective in baseball last season. He allowed a .195 wOBA and .192 xwOBA with the pitch last season while generating a crazy 55.8% whiff rate. Hitters actually batted below .100 (.089) against the pitch and even the expected batting average was below .100 (.097). This made it one of the most unhittable pitches in baseball last season.

Also in my earlier article, I wrote about how Reyes changed the shape of his slider. In 2019, the pitch had 2.5 more inches of vertical break than it did in 2021. Reyes gained 3.5 inches of horizontal break to make up for that. The St. Louis Cardinals right-hander first showed a different shape in 2020 as he added horizontal movement and lost vertical movement that year. Then, last year, Reyes added movement in both directions. The pitch had 7% more vertical break than the average slider last season and a whopping 92% greater than average horizontal break. It was also thrown over 86 miles per hour with a spin rate of 2588 rpms.

The characteristics of this pitch make it among the most dangerous offerings in baseball. Among pitchers who threw at least 300 sliders last season, Reyes finished seventh in wOBA (.196). The top two pitchers were Blake Treinen (.103) and Jacob DeGrom (.132). Those two switched places in the xwOBA rankings and Reyes finished in ninth (.192). Clearly this was an effective pitch, but there were a handful of names who had better results. wOBA and xwOBA don’t tell the whole story, though.

Reyes had the second lowest batting average allowed against his slider in the league (.089). This was only behind Treinen (.074). The flamethrower surpassed Treinen in xBA (.097), but he still finished in second place, behind only Braves reliever Will Smith (.095).

Reyes had a better whiff rate with the pitch than both Treinen and Smith and he again finished in second place, this time behind DeGrom. His 55.8% whiff rate was a touch behind DeGrom’s 58.1% whiff rate.

Finishing in second place in BA, xBA, and whiff rate is quite the feat. It is also notable that he was the only pitcher to finish in the top three in each category. Reyes’ slider was clearly one of, if not the most, unhittable pitches last season.

He fell down to the lower edge of the top ten in wOBA and xwOBA because he gave up more hard contact and walked too many hitters with the pitch. Reyes threw a comparable amount of sliders in the zone as Treinen and he actually threw more in the zone than DeGrom, but despite this, he had a much higher walk rate with the pitch. His 10.8% walk rate was nearly three times larger than Treinen’s walk rate of 3.9%. DeGrom walked an even smaller percentage of hitters with the pitch (1.7%) despite throwing almost 70% of his sliders out of the zone.

Slider are pitches that tend to induce hitters to chase outside the zone. Because of that, a pitcher can get away with throwing more of them out of the zone. Then, when a hitter chases a slider, it is nearly impossible to make hard contact.

So, Reyes has the right approach by throwing more sliders outside the zone. However, he needs to bear down when there are three balls. The right-hander likes to throw his slider in full counts. In fact, it is the pitch he throws most often in such situations. If he is going to do that, then he needs to be able to throw his slider in the zone or cause the hitter to chase. Ideally, he would live on the edge of the plate in these scenarios, but both Treinen and DeGrom threw a higher percentage of their sliders on the edge of the plate.

If Reyes is going to throw so many 3-2 sliders, he needs to be willing and able to challenge the hitter or hit a spot on the edge of the zone. He surrendered too many walks with the pitch and that is one of the reasons why his slider ‘only’ finished seventh in wOBA among pitchers to throw 300 or more sliders.

We have already seen how hitters basically can’t touch Reyes’ slider. If hitters are batting below .100 against the pitch, then he needs to be more aggressive with the pitch on full counts since if he misses his spot in the zone, he is likely to get away with it. Obviously, it would ideal if Reyes could improve his control and learn how to hit the edge more because the second reason why his slider wOBA was a little higher was because he gave up too much hard contact against the pitch.

Reyes allowed a barrel rate of 9.4% against his slider. For perspective, DeGrom allowed a rate of 4.3% and Treinen didn’t allow a single barrel against his slider all year. Reyes’ higher rate almost certainly was caused by him throwing more sliders middle-middle. According to Brooks Baseball, Reyes grooved 8.02% of his sliders last season, which was the highest percentage of any of his offerings. Brooks Baseball defines a grooved pitch as a pitch thrown middle-middle, obviously not a great location. DeGrom (2.83%) and Treinen (5.30%) both had much lower percentages.

This means that Reyes grooved 28 sliders last season. Brooks Baseball tagged Reyes for 349 sliders last season, while Baseball Savant had him throwing 350. I am going to use Baseball Savant’s 350 since the rest of the numbers will come from that site. Reyes threw 126 sliders in the zone last season (for an in-zone% of 38.9%). By grooving 28 of those 126 sliders, he grooved 22.2% of all sliders that he threw in the zone last year. That is not a good percentage. He needs to live more on the edge, even if his slider is borderline unhittable. By throwing it right down the middle, he is actually giving hitters a chance.

Reyes allowed four home runs against his slider and five home runs against all of his other pitches combined. The 27-year-old has a nasty slider, but he is prone to making mistakes with it. Outside of the home runs, Reyes gave up just four other hits against the pitch and they were all singles. The home runs are what inflated Reyes’ wOBA and bumped him into the lower half of the top ten in slider wOBA last year.

Fewer grooved pitches generally means fewer barrels and less hard contact. This is the last step that Reyes must take before his slider can rival that of DeGrom and Treinen.

It’s not like I’m talking about a pitch that Reyes desperately needs to improve. His slider was an excellent offering in 2021, and it was among the best sliders, and even the best pitches, in baseball. Still, he has room for growth with the breaker, and with some slight command improvements, he could potentially have the best slider in baseball. The pitch is already nasty, now Reyes needs to be able to place it where he wants it more often and it will become even more devastating. It is already unhittable, but fewer mistakes would give hitters absolutely no chance at doing anything good when they see his slider.

Basically, these are not pressing improvements that Reyes needs to make, but they could allow his slider take the next step from elite to a top two or three slider in the game. Anytime a pitcher is being compared to Treinen and DeGrom (as I have done throughout this article), he is doing something right. Still, it is not surprising to see that the one thing holding Reyes’ slider back a bit is occasional lapses in command.

I have already made the argument that Reyes should throw more curveballs because the pitch has great movement, velocity separation, and opposite spin to his fastball. Along with a slider that was thrown 28% of the time and a four-seamer that made up 30.8% of the flamethrower’s arsenal, it is clear that Reyes has the stuff needed to become a starter. He needs better control, but he does have a proper arsenal. Unfortunately for him, control is paramount when throwing at least half the game.

Reyes could also bump up his slider usage. If it is one of the best pitches in the game, then he can afford to be more aggressive with it. This may mean dropping his sinker usage, since his four-seamer has a solid rising effect and plays well at the top of the zone. A wipeout slider that dives out of the zone is a perfect complement to this, and if Reyes doesn’t end up moving into the rotation, then he could be a really effective two-pitch pitcher with the occasional sprinkling in of some other offerings.

Having a top ten slider in baseball, with the potential for top two or three, gives Reyes quite the safety net. It’s a pitch that can give him success in any role. With elite velocity, all he needs is better control to see his game take a major leap and his slider rival that of Jacob DeGrom.