Let’s Talk About Mike Foltynewicz’s Slider

Mike Foltynewicz
Mike Foltynewicz retired the first 13 batters that he faced before allowing a solo home run in the fifth inning of Monday's Braves-Phillies game in Philadelphia. (Photo by Mitchell Leff/Getty Images)

The Atlanta Braves are 90-56, 9.5 games up in the NL East, and now have a single-digit magic number to clinch the division.

Mike Foltynewicz’s season-long ERA and FIP both start with a five.

Those two sentences both being true for the 2019 season are, honestly, incredible.

As the ace of the 2018 division-winning Braves, much was expected of Folty this season. He had finally reached the potential so many dreamed about when he was a prospect and was ready to take his place among the best starters in baseball.

Then this happened:

Before spring training barely even got started, Folty was already dealing with a setback. Mike was shut down for the rest of spring training, and right from the jump, he was behind schedule. Luckily, the injury wasn’t that serious. Folty was able to start the season with AAA Gwinnett, get stretched back out, and join his teammates in Atlanta by the end of April.

But right from the beginning, something was just…off The Folty that returned from injury wasn’t the same guy that carried the pitching staff the year before. In his first 11 starts of the season, Mike produced an astonishing 6.37 ERA and a 6.14 FIP. The command wasn’t as sharp, the negative emotions he had done so well controlling last season were back to being a problem and, most importantly, his stuff just wasn’t as good. Specifically, his slider.

This was Folty’s 2018 slider:

A sharp, exploding slider that right-handed hitters could barely touch.

Now compare it to Folty’s 2019 slider:

A flat, lifeless pitch that starts over the middle, stays over the middle and gets cranked for a 3-run HR.

To put some numbers to the difference in these two pitches:

  • In 2018, Folty’s slider had a pitch value of +22.9 runs, fourth-best in all of baseball.
  • Between April and the end of June 2019, Folty’s slider had a pitch value of -5 runs, one of the worst in baseball.

A pitch that had been a weapon in the best season of Mike’s career had become a liability in the worst season of his career.

I used June as the endpoint for that last stat because, well, that’s when Folty got demoted. With playoff and even World Series aspirations in front of them, Atlanta’s game 1 starter for last year’s NLDS was optioned to AAA.

Braves’ GM Alex Anthopoulos was obviously asked about the move after it happened, and while the talking points from reporters were about Mike’s emotions and his elbow, Anthopoulos made two things crystal clear. Mike was healthy enough to pitch, and Mike needed to get his slider back.

After the demotion, The Athletic’s Jeff Schultz caught up with Folty to get his thoughts on everything that happened. It’s a terrific piece I fully recommend checking out but there’s a specific quote that needs to be included here. Schultz was asking about the Spring Training elbow scare and the fallout from it and this was Mike’s response:

“Somebody told me a long time ago there’s a difference between being hurt and being sore, and I really took that to heart,” he said. “But when something like that happens, it’s in the back of your head. If you rip a slider, what’s going to happen?’ It makes it tough to go out there and pitch 100 percent. I may have just tweaked my mechanics a little bit. That can be f’in up everything.”

While most of us had concentrated on whether Mike was physically healthy, he admitted for the first time it was the mental hurdles of the elbow injury he was struggling with most. Now bone spurs aren’t anything but as Folty noted, he pitched with them all of last year. But after the injury this year, when it was time to “rip a slider,” he was having trouble fully committing. And it showed it the results.

Later in that same piece, on the fear of pitching with the injury, Mike concluded, “I’m just going to have to learn to throw the slider, let it go and hope for the best.”

This was his plan for redeeming a seemingly lost season. Throw the slider, let it go, and hope for the best.

On August 5th, Kevin Gausman was claimed on waivers by the Cincinnati Reds and Mike Foltynewicz found himself back in Atlanta’s rotation. And since he’s been back, we’ve started seeing glimpses of the Mike Foltynewicz from 2018. Flashes here and there of the terrific starter he was a year ago. And one main reason for that is he’s starting to find his slider again.

Before Mike got demoted, his slider had the least horizontal movement of his career. This graph from Brooks Baseball illustrates the point:

At his best, Folty’s slider was moving, on average, around 2.5 inches horizontally. From April to June of this year, it was moving less than half that (1.21 inches). If you go back up top and look at that gif of the Ozuna HR, you can see it. It would start in the middle of the plate and just stay there. And that wasn’t a cherrypicked instance. I had dozens to choose from.

But since he’s been back, Folty’s slider has been back up to averaging 2.88 inches of horizontal movement, which even better than last year’s number. It seems he’s a little more willing to “rip it.”

Of course, it’s not all about movement. Location matters too. Before his demotion, Folty’s slider was living in the middle of the plate. Here’s a pitch heatmap of every slider he threw between April and the end of June:

You can see a dangerous collection of pitches right in the middle of the plate. And not just in the middle of the plate, but belt-high in the middle of the plate. These are meatballs that usually get destroyed by major league hitters.

But since his return, it’s looked more like this:

As you can see, he’s moved the pitch closer to the left-handed batter’s box, which is where right-handed pitchers typically want their slider. You can also see a greater concentration towards the bottom of the zone. He still occasionally leaves one in the middle, but it’s not where the pitch lives anymore. And, of course, movement helps with location. More and more, he’s getting the pitch to the edge of the zone and below it.

This is a perfectly placed one vs Toronto:

And another one against LA:

Before Mike got optioned to AAA, he was giving up a .585 slugging percentage on his slider, which is what Pete Alonso slugs all the time. But since his return, opponents are slugging .333 against it.

I mentioned earlier, in his first 11 starts, the pitch value on Folty’s slider was -5 runs after being +23 runs last year. Well in the 7 starts he’s had since his return, it’s been valued at +1.5 runs. Stretched over a full year, that’s a good pitch. It’s not back to being the wipe out weapon it was in 2018, but it’s also an upgrade from the absolute disaster it was in early 2019. At the moment, it’s a solid option for him. And that’s progress.

It’s probably not a complete analysis unless I mention Mike’s overall numbers have improved as the slider has. Since his call up in early August, Foltynewicz has a 2.95 ERA and a 3.99 FIP. Neither of those numbers starts with a five. Or a six. Mike has also added four percentage points to his K%, going from 19% to 23%. And that all makes sense. His slider is one of his primary weapons, and it’s logical that as it improves, so would he. We’ll see where it goes from here.

Everything is easier for the Atlanta Braves with a good Mike Foltynewicz and everything is easier for Mike Foltynewicz with a good slider. Atlanta is hoping to see more of both. Especially with what lies directly in front of them: October.


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