Regard: Buck Farmer’s Slider and Probably Changeup
Right-handed Detroit prospect Buck Farmer, making his major-league debut shortly after making his Double-A debut, has just completed his first inning of work. With a view to edutaining the public and also securing internet clicks, the author presents footage below of Farmer’s secondary pitches.
First, his slider, to Pittsburgh’s Russell Martin:

And second, probably his changeup at 83 mph, to strike out Martin:

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that second one is a backup slider, you can see the dot.
That’s what I thought as well.
dot?
on the ball itself, generated by rotation
It isn’t a slider. The spin doesn’t have the telltale spin of a slider. Moreover, Farmer pronates his forearm. A slider requires forearm supination. The grip is also definitely not a slider grip. He is gripping the ball more tightly, and in the palm of his hand. A slider grip is held more in the fingers and fingertips.
I think most people would call this pitch a sinking change. Farmer is turning the ball over at his release with pronation similar to what is used with a true sinker. But he is gripping the ball more tightly in the palm of his hand than a pitcher would with a true sinker. Some people might call this a screwball, but the forearm pronation isn’t as severe as one would typically see with a screwball, and therefore there isn’t as much rotation and movement as one would see with a screwball.
This is the right answer. It’s a slider grip, and you can tell from the release that he comes around it (the pronation you see is after release, during the follow through).
Also you can tell by the way Avila catches it that he was NOT expecting the ball to move like that.