Analyzing Jameson Taillon’s Slider, a pitch he didn’t even have 2 months ago


A lot of people know Jameson Taillon as the guy who had cancer and only missed 5 weeks of baseball. Others know him as the guy that was picked between Bryce Harper and Manny Machado in the 2010 MLB Draft. Fewer know him as a pitcher; the fastball/curveball guy with power stuff and good command. 

If you're unfamiliar with Taillon then don't worry because the scouting report on him is out of date. Taillon has a slider now. And he throws it a lot. 

Rolling averages give a day by day stapshot of what the last X-number of games have looked like. In this case each datapoint represents how often he threw that pitch over the last 5 games. 


This chart shows his 5-game rolling average for pitch usage. The red line is his slider that came out of nowhere to become his most used breaking pitch. 

I first learned about this develop from Rob Biertempfel's article for required) in which he chronicled the development of Taillon's slider in a couple of bullpen sessions in May with the help of teammate Chad Kuhl and pitching coach Ray Searage. The big takeway from the article is that Taillon is extremely talented to be able to learn a pitch and get it major league ready after just a couple of bullpen sessions. 

A few weeks and 8 starts later I thought it worth looking at Jameson Taillon’s slider to see how the experiment was progressing.

Let's start with an at-bat against Rhys Hoskins from his most recent start on July 7th. 

Pitch 1: Fastball(96 MPH)

Strike 1 with the heater. The catcher Diaz, wanted it away and Taillon missed the location by a good bit. 96 MPH certainly helps him get away with this especially since Hoskins seemed ready to jump on it. Taillon was 18 for 22 on first pitch strikes in this game. 

Pitch 2: Curveball(82 MPH)

Completely nasty curveball to get ahead 0-2. Hoskins has to be thinking he will see this pitch again. 

Pitch 3: Slider(90 MPH)

Here's your first look at the new slider. The velocity places it right in the middle of his curveball and fourseamer for some good diversity. More horizontal than his curveball but doesn't move a ton either way. As for the sequence you can't throw a better 0-2 pitch. The previous curve sets up the slider perfectly here because of the smaller vertical break. Hoskins froze on this thinking it was another curve that would drop well below the zone. Instead the borderline call goes Hoskins' way. 

Pitch 4: Fastball(96 MPH)

Another fantastic pitch from Taillon and a great take by Hoskins. Taillon barely missed his mark and while the count is now back to 2-2, Taillon is still in the drivers seat as he's resisted going back to the knee-buckling curveball. He also hasn't thrown anything away yet. Tons of options for him and Diaz to choose from. 

Pitch 5: Slider(89 MPH)

I didn't think he would throw the slider before returning to the curve but then again, Hoskins did whiff on a slider in his first at-bat of the game. Diaz wanted it low and away and Taillon missed by enough that it ended up jamming Hoskins in. First big mistake from Taillon in this at bat and our first look at a poorly executed slider. 5 pitches into the at-bat and Taillon still hasn't gone away. 

Pitch 6: Fastball(95 MPH)

Diaz is like, "maybe if I set up in the dugout he'll finally hit the outside corner." Compared to the other pitches this was a fairly easy take. But you can tell from Hoskins' hips that he was not ready to deal with 96 on the outside corner. Another good pitch from Taillon but now he's out of wiggle room. 

Pitch 7: Slider(90 MPH)


Remember two pitches earlier he hung a slider and got away with it, yet he trusts that pitch enough to come back on a 3-2 count. This time he executed much better. Being able to get whiffs in the zone makes his slider a great weapon for a three ball count. The curveball that Hoskins was waiting 4 pitches to see again never came.

That’s a 7 pitch at-bat against one of the games most patient and dangerous hitters and he threw 3 sliders. 

The sample size of his slider usage isn’t huge but the early returns are promising. By fangraphs pitch value metric it’s well above average. It's actually been his most valuable pitch since May 27th, the day his slider was fully unveiled. 

Taillon's Pitch Value Totals Since he began throwing his slider(8 starts/48.2 IP)

Measured in runs, "Pitch Values" are a way to assign a run value to a specific pitch type based on how hitters have performed against that pitch. Numbers courtesy of

8 starts is admittedly not a huge sample to be looking at pitch value but it's all we have for his slider. For example: his fastball being so poor is strange but almost all of that came from one bad start against the Dodgers when it racked up -2.4 runs alone. When you take all of 2018 as the sample, you find that his fastball is fine(+0.1) and his change-up is not(-4.0).

The point of that graph is to show that his slider belongs. 8 starts is long enough for teams to know they will be seeing a slider from Taillon and yet it's still working(6 whiffs on 19 sliders his last time out). 

The cool thing about this new pitch is that it isn't just a tool against righties.

Pitch Usage Versus Lefties

Information courtesy of

Pitch usage versus righties


He may be throwing it a monstrous 33% against righties but the 18% clip against lefties is still significant, especially since his change-up is nothing special.

Here he is using his slider to steal a strike when down in the count to a lefty. 


Now here's a more prototypical use to get the strikeout against another lefty. 



Now for a closer look at what is happening when he throws it let's check out his swinging strike rate:

Fourseam: 10.85%

Sinker: 6.99%

Slider: 17.24%

Curveball: 13.21%

Change-Up: 8.11%

His slider has instantly become his best swing-and-miss pitch. And look at the affect that has had on his overall Swinging Strike% in 2018(reminder that the MLB avg. for SwStr% is 10.7%:

before starting to throw his slider = 9.2%

After starting to throw his slider = 11.1%

Here’s a graph illustrating just this increase. A rolling 10 game split showing the spike in whiffs since he debuted his slider.


He hasn't induced swinging strikes like this in his whole career. 

Swinging strikes are a strong precursor to strikeout development especially when you can pin the increase on a specific change that the pitcher is making. It stands to reason that if a pitcher starts throwing a pitch that gets 17% whiffs and throws it in place of pitches that get fewer whiffs(say his changeup that only gets 8% whiffs), his overall whiff rate will go up.

So even though his overall K% hasn't changed much since he started throwing the slider(only a 0.6% difference) I expect that is mostly just noise or sequencing issues that he will fix with time. Taillon has the stuff to be at least a strikeout per inning guy(only 8.08 K/9 in his career so far).

Finally, now that we know all about his slider let's see how his overall numbers have changed since he added the new pitch. 

The following are Taillon's stats split up between the 51.1 innings before the slider and the 48.2 innings after the slider. 

Before: 4.56 era -- 4.14 fip -- 3.90 xfip -- 14.6% k-bb% -- 47.7% groundball%

AFTER:  3.51 ERA -- 3.09 FIP -- 3.39 xFIP -- 16.5% K-BB% -- 52.5% groundball%

These improvements may not be eye-popping but I’m pretty damn impressed. That FIP places him 13th best in baseball among starters over that time frame and that's without the jump in strikeouts that I expect will come with time. The other thing we haven't even touched on yet is the groundball rate. 52% ranks 11th in baseball and shows that his slider isn't negatively impacting his ability to keep the ball on the ground. Lastly, his BABIP is .295 over this stretch(in line with his career number) so it isn't like funky batted ball luck has made these numbers look better. 


We’ve seen a lot of sliders today. Not all of them perfect but his confidence in the pitch and his willingness to throw it in all counts and to lefties tells me it is only going to get better. Taillon’s arsenal is officially 3 deep and that has me very excited for his continued development into the ace he was drafted to be.

Lucas Hooper