Vinnie Pasquantino and Statistical Divergence

In some ways, Vinnie Pasquantino has been everything I wanted since he came to the big leagues. His approach at the plate is consistently good, so he walks a lot and strikes out at a fairly low rate. When the ball is put in play it tends to be hit hard. That mix is what I was looking for, and it is usually a recipe for success. However, Vinnie's .211/.317/.333 is not at all what the Royals need from their rookie slugger. Expected statistics are something that I like a lot, and I know the statistically disinclined tend to misunderstand or outright hate them. I would like to use the divergence in Pasquantino's outcomes so far versus his expected outcomes to talk about the good and the bad of these statistics.

Baseball Savant has Vinnie's xBA (expected batting average) as .286, much better than the .211 he is carrying. Similarly, his expected slug is .507, a full .164 above his actual. From

"Each batted ball is assigned an xBA based on how often comparable balls -- in terms of exit velocity, launch angle and, on certain types of batted balls, Sprint Speed -- have become hits since Statcast was implemented Major League wide in 2015. (As of January 2019, xBA now factors in a batter's seasonal Sprint Speed on "topped" or weakly hit" balls)"

Each ball put into play is given a probability of becoming a hit (and for slug a certain type of hit), and then you accumulate the expected values of said probabilities, and you have what a player who had put all of those balls in play should theoretically look like statistically speaking. There is an adage I have always seen attributed to British statistician George E.P. Box that goes, all models are wrong, but some are useful. I find this model useful, but as with any statistical model, it is imperfect. So, has Pasquantino been super unlucky, and should he have a line more like .286/.392/.507 as the model states?

One thing really stands out to me in the early going for Pasquantino. His batted ball profile has so far not translated to the big leagues. He is pulling the ball a little less, hitting more ground balls and pop-ups, and fewer line drives than he did in the minors. He has been hitting the ball very hard, but a lot of those hard-hit balls are on the ground and into the shift. Here are all his balls with exit velocities at or above 100mph, sorry it is linked, and I could not for some reason get it to publish in this article directly.

There are 27 in total, and 9 of them are outs hit on the ground. One of the gray dots that looks like he grounded into the shift is actually a very high fly ball. So, 33% of his 100mph and up balls struck are just ground outs. There are also 4 ground ball hits. That means his ground ball rate on these is 48.1%, well above the 41.1% ground ball rate he has on the season, and the ground ball rate he had in the minor leagues that was always in the low to mid-30% range. Theoretically the model should to some extent account for this, but again, they are imperfect, and he is a slow runner (16th percentile in sprint speed). It is possible that more of these should be hits, but the one he hit into the shift last night looked super routine and had an exit velo of 105.8 mph.

So far, Pasquantino’s ground ball rate is not great, but it is not extreme either (Aaron Judge is within half a percent of him). It just looks like the hard contact is ending up in ground balls and pop-ups more often than usual, and we won’t see the numbers start improving drastically until they start being line-drives more often like they were in the minors. I am expecting this to happen, he looks comfortable at the plate and his walk and strike out rates have come across close to as you would expect, so he just needs to adjust to the pitches he is seeing, which include mostly off-speed and breaking stuff.

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