In recent years, the slider has become the most talked about pitch in baseball. Pitchers are throwing it more and more, and hitters are trying to keep up.
Tom Verducci wrote about this phenomenon for Sports Illustrated again in July.
Hitters are hitting just .209 against the slider, the lowest against any of the five pitches thrown at least 2% of the time. Pitchers and their coaches are tracking the data. For the first time in recorded history, fastballs (not including cutters) are being thrown less than half the time. Since 2015, which marked the beginning of the Statcast era, fastball usage has dropped from 57% to 48%. Almost all of this decline can be attributed to an increase in sliders.
The use of sliders has increased in each of the last eight seasons. In 2022, the slider accounted for just under 22% of all pitches thrown (per Baseball Info Solutions).
The Philadelphia Phillies, however, have used that particular pitch just 16.2% of the time this year. Only the Arizona Diamondbacks have thrown fewer sliders.
To make matters even more confusing, Phillies pitchers are actually pretty good at throwing sliders. They have the fastest sliders in the league this season, averaging 86.2 MPH. While velocity isn’t as important to sliders as it is to, say, fastballs, an 86 MPH slider is a bad pitch.
Only 11 teams in baseball average over 85 MPH on their sliders. Only two average more than 86 MPH. Research has shown that almost all sliders faster than 85 MPH are effective pitches, regardless of form/movement.
According to the Pitch Value metric at FanGraphs, Philadelphia ranks 16th in baseball in total value created with their sliders, even though they rank 29th in the rate of sliders thrown.
In other words, the problem isn’t that the Phillies are bad at throwing sliders. Something else is happening.
Well, more precisely, three things are happening:
- Aaron Nola is doing a lot.
- The starting rotation is fluctuating a lot.
- Zack Wheeler and Bailey Falter are confused.
Let’s take a closer look.
Aaron Nola has played more games than any other Philadelphia starter this season. He is third in the Majors in innings pitched and sixth in strikeouts. His 2,653 pitches account for more than 13% of all pitches the Phillies have thrown.
Of all those pitches, there have been fastballs, curveballs and changeups, but never a slider. Nola doesn’t throw a slider. He never has.
In this day and age, that’s unusual. Of the 111 starting pitchers with at least 100 IP this season, only 16 have never thrown a slider.
By not throwing a slider, Nola is lowering the team’s slugging rate. It’s a pretty simple fact. When the hardest starter on a certain team doesn’t throw a certain pitch, then that certain team won’t throw that certain pitch as often.
Indeed, if Nola were to throw sliders at the league average rate for a starting pitcher, Philadelphia’s slugging rate would jump up to 18.7%. That would rank 24th in the league.
However, this factor alone cannot clearly explain why the Phillies use so few sliders. With Nola out of the picture, Philadelphia would still have a low sliding scale. Additionally, several other teams also have starting pitchers who don’t throw that particular breaking ball, and they still use more sliders than the Phillies.
So what else is going on?
The starting rotation
The Phillies have a struggling rotation this season. Their starting pitchers have thrown 780 times, which ranks fourth in the Majors and second in the National League. Therefore, the team has only had to throw 460.1 IP, which ranks 28th in baseball and dead last in the NL.
Why does this matter when we’re talking about sliders? Because relievers throw more sliders than starters. More. In 2022, relief pitchers have thrown sliders an incredible 25.9% of the time, while starting pitchers have used the slider for just 18.9% of pitches.
That means teams that get more innings from their starters can be expected to use fewer sliders. Since Philadelphia has a rotation full of workhorses, they don’t need to rely on their bullpen as much as most teams. Fewer queues mean fewer sliders.
Phillies relievers actually throw more sliders than average. They use the field 26.3% of the time, which ranks 13th in the sport. But because they aren’t called upon as often as most relievers, they don’t make up nearly as much of the team’s overall pitches.
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If the bullpen and starting rotation had both thrown a league-average number of innings while their sliders continued to throw at the same rates, the team’s slugging rate would increase from 16.2% to 16.9%. That would still rank 29th in the league, but it’s a noticeable jump.
If, in addition, Nola were to throw sliders at the league average rate (assuming his pitch count stayed the same), the team’s slugging rate would jump up to 19.4%. That would rank 21st in baseball and not that far off the MLB average of 21.8%.
Those two factors, when combined, do a pretty good job of explaining why the Phillies have thrown so few sliders this season. But we can still go deeper.
The blush, as we have already established, is using sliders at a completely normal rate. The starting rotation ranks last with a 9.7% slugging rate, but a large part of that can be explained by Aaron Nola’s pitching staff.
However, even if Nola were to throw sliders at a league-average rate, Philadelphia’s rotation would still throw fewer sliders than most teams.
Besides Nola, there are two Phillies starters who don’t use a lot of sliders. Zach Eflin cut back on his slider usage this year in favor of his curveball. Ranger Suarez is also throwing fewer sliders, having added a cutter to his repertoire.
On the other hand, Kyle Gibson is throwing a lot more sliders this year than when he came over from Texas last season. Noah Syndergaard is also throwing the slider much more often than he did with the Angels earlier this year. Both throw more sliders than the average starter, especially Syndergaard.
More or less, Eflin, Suárez, Gibson and Syndergaard are incompetent for each other. Therefore, the two starters left to focus on are Zack Wheeler and Bailey Falter.
According to Baseball Info Solutions, Wheeler throws a slider 14.7% of the time, well below the league average. Falter doesn’t throw sliders at all.
However, according to other pitch tracking sources such as Pitch Info and Baseball Savant, Wheeler throws his slider almost 28% of the time, while Falter uses a slider as his secondary pitch. What’s up with that?
Well, according to Baseball Info Solutions, both Wheeler and Falter throw a fastball. But as far as Pitch Info and Baseball Savant are concerned, neither has a cutter in their arsenal. Instead, almost all of those cutters are categorized as sliders.
This is more than a simple error or miscalculation from any pitch tracking source. Both pitchers, Wheeler and Falter, pretend to throw a slider AND a cutter However, both admit that the two fields can seem quite similar.
Wheeler’s cutter/slider is so fast that it confuses pitch tracking sources, which can’t decide if it’s a fast cutter or really fast slider. Falter, meanwhile, has so little movement in his cutter/slider that pitch tracking sources apparently can’t tell if it’s a low-movement slider or just a slow cutter.
Ultimately, however you categorize their offerings, Wheeler and Falter are throwing pitches with slider-like quality as their secondary weapons. They both know how important the slider is in modern baseball.
If we counted all of these fumbles as sliders rather than cutters, the slugging rate for Phillies starters would go up to 13.2%. This is a huge increase from 9.7%.
Then, if we add to that number a hypothetical Nola throwing sliders at the league average rate, Philadelphia’s starting rotation would throw sliders 17.3% of the time. That would rank 18th in baseball.
Suddenly, the Phillies’ slugging rate doesn’t seem so low after all.
Sliding it all together
So are the Phillies behind the curve — or should I say, behind the curve — on this one?
It certainly doesn’t seem that way. A closer look at the data shows that there really isn’t any cause for concern.
- Aaron Nola has thrown more than 13% of all Phillies pitches, none of which have been sliders.
- The Phillies bullpen has fewer innings than any other NL bullpen, and bullpens tend to throw more sliders.
- Zack Wheeler throws a slider too fast to be mistaken for a cutter. Bailey Falter throws a slider that could be mistaken for a slow cutter. Both areas have proven difficult to categorize.
Even taking all of that into account, Philadelphia still throws fewer sliders than the average team, but not so few that it stands out as an oddity. The slider is on the rise, and there’s no reason to believe the Phillies are falling behind the trend.
All pitch data from Baseball Info Solutions, via FanGraphs, unless otherwise noted.
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