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Mound Visit: Early returns on Keller’s ‘stuff’


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STATE COLLEGE, Pa. -- Mitch Keller, the top prospect in the Pirates' system, has debuted this year — much earlier than expected. The 23-year-old has just 21 AAA starts over two seasons, so with such a rushed timetable, how are we to properly judge our first look at a hurler who, at the very least, is projected to slide in as a rotation anchor?

Keller has had a rocky go of things over his first three starts. Incremental improvement has been seen, to be sure. Yet, 12 innings is simply not enough to form any logical conclusions about the young right-hander.

But what we might just be able to do with this small set of data is offer a few educated opinions on the state of his "stuff."

That term is thrown around wildly in baseball circles to describe a pitcher's repertoire. In its previous life, the term referred chiefly to a pitcher's velocity, until a natural evolution occurred that invited movement to the party. In today's game, to get a complete look at a pitcher's offerings, one must avoid a myopic view at all costs.

What follows is an exercise in drawing conclusions on Keller's stuff from our small sliver of samples. We'll take a look at each of his pitches, complete with supporting data for each.


Keller's four-seamer was rated as his best pitch, taking home a 65 rating on the 20-80 scale. It has good, natural sinking action (but is not a true sinker), and it certainly has the organization's trust with a 62 percent usage across his first three starts.

It carries slightly above-average spin at 2,473 rpm -- league rate is 2,274 -- allowing him to locate it all across the strike zone with confidence. High spin strikes have been a growing trend in baseball over the past seven years, as pitchers have learned that a higher spin can fool hitters who think a four-seamer is about to start dropping toward the bottom of the zone at any moment.

This chart shows the spin rate of all swings and misses from all MLB starters on four-seam fastballs. "Total pitches" refer to all of a pitcher's pitches, fastball or otherwise.

As you can see, there is about a 50/50 split between low-spin swinging-strikes and high-spin. However, pitchers who are fastball-heavy seem to benefit from higher spin in terms of getting a hitter to whiff. Keller has a small sample size here, but is well positioned relative to his peers with similar spin.

Despite what's written above, velocity still has a seat at the head of the table in terms of fastball effectiveness, and comes into sharper focus when paired with good spin. Here, Keller finds himself on the right side of the trend line, with good spin coupled with high velocity. The result is more swings and misses, which I'm told is a good thing.


I grouped these two pitches together as, frankly, they have not been seen enough to warrant their own entries.

The curve has been long described as Keller's second best pitch, with a chance to be special. A quick look at the curves he has thrown at the big league level shows that he is still working to harness it properly.

Simply put, when Keller's curve moves, it moves. When it doesn't, it sure can hang. That's true for nearly all of the curveballs thrown in major league baseball, but Keller's baseline -- a 2,776 rpm spin rate -- begs for him to execute it properly in order to put it on display as a premier pitch.

These three curves show the range of Keller's bender. The first pitch hangs quite a bit, and is saved only by a good jump from Corey Dickerson. The second one is a bit better -- even if Josh Donaldson does not bite, the movement is there. The third pitch against future Hall of Famer Miguel Cabrera is a great example of good movement that hits just the right spot.

Keller's changeup has always been a thorn in his side, with the common criticism against him being a lack of a third pitch. To that end, the Pirates have spent considerable time and development in trying to bring along Keller's changeup. Results are still mixed.

For one, there is not much natural movement in his change, which can cause it to come out a bit flat out of his hand. Without much change in velocity between it and his four seam fastball -- Keller averages 90.76 mph on the change, opposed to 95.68 mph on the fastball -- the pitch can look very hittable even when it lands in a desirable location, such as this one:

The good news is that the curveball and change are two pitches that can be greatly impacted by little tweaks, namely grip changes and release points. I would fully expect Keller to take a good bit of homework back with him to Indianapolis.


Ah, the new kid on the block. Keller added a slider this year out of the blue. Remind you of anyone?

Although he did not have the near-instant success that Jameson Taillon had when he introduced his version, Keller's slider -- much like his curve -- has a good foundation for success, with an average 87.99 mph velocity and 2,682 rpm spin.

Yet, the biggest platform for Keller's continued slider success comes from his ability to bury it properly. Here's a look at where his sliders have landed thus far:

On the back foot against left-handed bats? Check. Falling away from a right handed hitter? Check.

Though this heat map shows success, Keller has shown a tendency to hang one on occasion:


In the first pitch here, Keller's slider hangs just enough for Ozzie Albies to take it for a ride before Keller is ultimately saved by another good Pirates outfielder's jump, this one from Starling Marte. Such is life for a slider in the major leagues, just a few inches changed between offerings can produce dramatically different results.

And there, in those inches, lies the widest plot of land in which Keller's slider can continue to grow. His average horizontal break on the pitch of 4.5 inches is only 0.9 inches better than the MLB average; while his vertical drop of 34.5 inches is only 0.7 inches better than the mean. This is ripe for change, and as Keller throws more of them, he will find the right mix of grip and spin.

Mitch Keller's debut was hotly anticipated by many going into the season. Though the results have been mixed, the stuff has a clear floor for success. Though the ceiling is in flux, the Iowa product has a ton to work with to get there.


June 19: Advanced fielding stats and you
June 18: Crick's slider is a sight
June 17: Saving Polanco’s summer
June 14: Brault steps up

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