How Much Extra Credit Should We Give a Young Lefty Starter?

Edwin Escobar, who came from the Giants in the Jake Peavy deal, debuted with the Red Socks on Tuesday. One inning of work is not enough to know much other than perhaps velocity, but that point alone started a discussion. He sat just under 92 mph, and once you correct for his appearance coming out of the bullpen, you might say he had average velocity. I even said this, on twitter. And Mike Newman responded:

@enosarris I had Escobar 91-93… That's plus velo from the left side.

— Mike Newman (@MikeNewmanRS) August 28, 2014

I’ve heard this before. I’ve thought it maybe untrue, for whatever reason. So I decided to check out a few splits among starters this year.

Limiting the pool to only those that had started in more than half their appearances, I took a look at some simple splits:

Right-handed starters: 91.9 mph average fastball, 19.5% K, 7.0% BB
Left-handed starters: 90.6 mph average fastball, 20.3% K, 7.1% BB

So if Escobar could sit over 91 mph as a starter, his velocity would indeed be above-average for a lefty starter. Of course it’s an issue of supply, as only 30% of the sample was left-handed. That means fewer 95 mph guys, fewer Danny Salazars, fewer chances at big velocity.

But the higher strikeout rate for lefties gives us a little pause, no? Over the course of thousands of plate appearances, you might actually see an effect from a .8% difference in strikeout rate. It’s a decent sample, too, with 71 pitchers in the lefty side of the ledger. And although the effect was much smaller last year (.2%), lefties still struck out more batters than righties.

Even if the strikeout rate last year was the same for lefties and righties, you’d think that lefties should strike out fewer batters for a few reasons. For one, they cede the platoon advantage to more than 2/3 of the batting population, since switch hitters add to right-handers to form a formidable obstacle. And for two, if they have less velocity, they should have fewer strikeouts — we’ve related velocity to strikeouts here before.

It could be survivor bias. To make it as a lefty starter, maybe you have to do things to overcome the platoon advantage the batters have against you, and those things lead to more strikeouts than you might expect, given their velocities.

Could pitching mix be a key to the survival of the lower-velocity lefties? Looks like it. Here’s what lefty and righty starters are throwing this year:

Guess which pitches have the highest traditional platoon splits? Yeah, sinkers and sliders. Changeups have the best reverse platoon splits, which is definitely important to a lefty starter. Changeups also have the second-highest average swinging strike rate among regularly-thrown pitches (and four-seamers get more whiffs than two-seamers).

What does any of this mean? For one, you do have to give a lefty with similar velocity as a righty some extra credit for his handedness. There are fewer lefties, and we can see that there are therefore fewer high-velocity lefties.

And for another, you want to think about the platoon splits of a lefty’s pitching mix a bit more than you might with a righty. That lefty will face an opposite-handed batter more often than his right-handed counterpart, and in the past, at least, that’s meant it’s been important for the lefty to have a changeup. After all, since Wade Miley has been throwing his changeup more, not a single lefty remains on this list of two-pitch starters.