STATE COLLEGE, Pa. -- Mitch Keller will return to the big leagues Monday in Anaheim, Calif., as he'll makes his fourth start for the Pirates, his first since June 18.
Perhaps now, after putting together a solid body of work since going back down to Class AAA Indianapolis, Keller will finally be ready to show off his curveball a bit more. In his three previous big-league starts, Keller three 106 four-seam fastballs, 35 sliders and just 15 curveballs. Eight changeups were thrown in for good measure.
Having just added a slider this season, it should come as no surprise that Keller is utilizing it more, to figure out its viability both in the minors and the majors. Still, the curveball has always been considered to be his second-best pitch behind his fastball. So why hasn't he shown it a bit more?
The answer is both simple and complex.
In looking at when Keller spins these curves, we see that he "let loose" in his last start -- the June 18th appearance -- with a whopping 10 curveballs thrown. Though the sample is maddeningly small, let's see if there are any takeaways to be had.
In fact, we can perhaps see everything we need to see in one at-bat. The Tigers' Christin Stewart faced Keller in this game, and the young hurler offered three straight curveballs to him. Let's look at the entire at-bat, and then point out some items of interest:
Keller starts off the at-bat with a solid fastball for strike one. That's something he does well. His first strike percentage of 62.3 percent is actually a tick better than the MLB rate of 61 percent.
Keller comes back with a solid curveball at 0-1 to get to 0-2. Now, let's look at the next two curveballs up above. Notice anything similar about them? They are all coming after the same spot.
Stewart is a little bit more than a fringe MLB-type of player who strikes out 23.9 percent of the time, an inflated but not altogether balloon-like figure. But any player of his ilk, not to mention those that are legitimate MLB everyday players, can lay off of these two pitches consistently. A curveball works best when it is paired on either end by something completely different -- be it a harder breaking pitch or in this case, a fastball to finish off the at-bat.
Across all of MLB, the FA-CU (fastball-curve) or CU-FA (curve-fastball) pitch pairings produce the best xwOBA in at-bats that are decided within that pairing. That figure is .267. Simply put, if a curve is book-ended by heat, the chances of a successful at-bat for a pitcher is maximized.
I looked at a bunch of other points of data on Keller's 15 curveballs seen in the majors thus far, only to be bitten by the small sample size bug. Those 15 curveballs carry only a 6.7 percent swinging strike rate, but the data points are few and far between. No worthwhile conclusions can be drawn from his major league showings of the pitch just yet. Until that time comes, perhaps the best thing that Keller can do is put the pitch in a position to succeed.
For now, until Keller gives us enough data to go on, perhaps the best thing we can say about his curveball is that there is enough potential inherent in it that makes us salivate for more of them.
MORE MOUND VISIT
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Aug 2: Archer’s one item on his to-do list
Aug 1: Can Osuna’s power play?
July 31: Where’s the talent?
