For Francisco Liriano to be productive during his second stint with the Pittsburgh Pirates, his slider must play.

Technically speaking, Francisco Liriano’s contract with the Pittsburgh Pirates is of the minor league variety.

But in all likelihood, he has the upper hand in earning a 25-man spot out of Spring Training. He checks so many boxes for the club: a left-handed reliever who can spot start while still getting out left handed hitters with relative ease.

Yet for Liriano to be productive, his best pitch is going to have to stand up. That’s the slider, of course. While no one expects the pitch to be as deadly as it once was, it will have to serve as an approximation of its former self at the very least for Liriano to wring a few good years out of the time he has left in the game.

But man, what a pitch it was.

Then.... #FilthyFrankie

During his Pirates heyday of 2013 through 2015, Liriano ranked first among qualified left-handed starters in strikeouts finished off by a slider outside of the zone that was swung at and missed according to Statcast. Both by raw number (181) and percentage (10.6 percent), Liriano knew that he could induce a swing-and-miss strike with the slider nearly anywhere he wanted, when he needed it.

The pitch was effective beyond its swing and miss capability as well:

Everything seemed to be working for Frankie’s slider, and it masked his other pitches’ warts quite well. During that same 2013-2015 window, Liriano’s two-seam fastball never had a wOBA below .365, while his changeup fared a little better, posting wOBAs below .250 in ‘13-’14 before ballooning to .331 in 2015. These three pitches represented the bulk of his offerings, and when things started to go south with the slider....well...

Now... #OkFrankie?

The slider has certainly regressed since 2015, though the end result might not be as impactful as one might think.

First, a look at the dwindling returns on the slider when used on two strike counts, or when the hitter is behind in the count:

Of course, when news of Liriano’s signing broke yesterday, many pointed out that he could still be effective against left-handers, and breaking out his whiffs per swing from the slider against RHH and LHH bears that out:

Though the rate of regression is less steep against left-handed bats, there is a clear path towards middling returns seen here.

Yet the simple fact is...despite garnering less swing and miss with the slider, it has retained a certain floor of effectiveness. The pitch carried solid wOBAs of .284 and .266 in 2017 and 2018, respectively. The key difference is that when hitters make contact, the pitch gets tagged more often — a .350 slugging percentage against it in 2018 help make that point, as while it is not necessarily an inflated number on its own, it is significant when compared to how the pitch performed previously — even if his overall average exit velocity on the pitch came in at a solid 85.5 mph combined over those two years.

The pitch has lost some movement over the past three years and now finds itself a bit closer to the rest of the sliders in MLB:

If we look at the movement here, it’s no wonder the pitch is still effective against left-handed bats. It still carries enough movement to be tricky, yet right handers have more time to track the pitch. The movement figures shown here do not represent a wide gulf between Frankie and other MLB slider offerings, yet they are significant when talking left/right splits.

One last chart!

Here we see the effect that less swing and miss has in Liriano’s approach. With less at bats starting off at strike one, and less hitters being fooled into swinging outside of the zone, the drag on Liriano’s other pitches becomes more pronounced. He has had to throw his below-average two-seam/sinker more than ever before over the past two years as a result. In 2018 alone, it got slapped around at a .521 SLG/.419 wOBA/90.0 MPH EV clip.

That stat above that I highlighted in bold — amount of strikeouts garnered by a slider via swing and miss outside of the zone — might as well be a distant memory for Liriano. Over the past two seasons combined, he has but 40 strikeouts arrived at in this manner.

So What Now?

So what can the Pittsburgh Pirates do to resurrect Liriano’s slider? Perhaps the answer has nothing to do with the pitch, specifically. Sinkers still have a place in the game, especially for pitchers who rely on a slider as much as Liriano does (see Archer, Chris). Liriano’s sinker has been awful over the years, but it still carries good enough velocity (92.62 mph on average last season) to serve as a setup pitch.

On the edges of the strike zone — as defined by Statcast — Liriano has seen wOBA clips that are markedly better than his overall figures, even if the results are still a bit gaudy. Over the past six seasons combined, these pitches clock in at a .340 wOBA. That includes .299 in 2013, and a .383 rate in 2018. Perhaps a renewed focus on pitching to these spots can bring about better slider results.

God, if bringing back Liriano didn’t make it feel like 2013-2015 all over again, writing that last sentence sure did.

I’m sure there are going to be a myriad of other ways to elevate (figuratively speaking) Liriano’s slider that Ray Searage and Justin Meccage are cooking up with Spring Training just eight days away.

If they are successful, we may be looking back at the Liriano signing as more AJ Burnett than Ryan Vogelsong.