Luke Weaver made his Major League debut in 2016. After being called up in early August, he made 8 starts, never going more than 6 innings. He finished the year 1-4 with a 5.70 ERA. These aren't great numbers, but it was his first shot at this level—a substantial adjustment.
In 2017, he was called up a month sooner, in July. He made two appearances out of the bullpen before finally starting against the Diamondbacks on July 27th. It was a game reminiscent of his performance from the previous year. Since then, he has been nothing short of dominant.
In 4 starts, he has struck out 37 batters. Weaver has provided a huge lift to the Cardinals rotation the last three to four weeks. But how exactly has he done it?
It starts with his fastball, which he throws 57.43% of the time. Although it has essentially average velocity (94 mph), it generates more whiffs per swing when compared to other four seam fastballs. This is due in part to the vertical movement (one of my favorite aspects of a fourseam fastball) caused by a spin rate of 2220 rpm. This pitch has improved in the last year, going from an average vertical movement of 8.23 feet in September 2016 to an average vertical movement of 9.41 feet in September of this year (This is a small sample size, but I though I would at least draw attention to the improvement).
This year, a main difference in his repertoire has been the changeup. In 2017, his changeup has resulted in a groundball almost 13% of the time (BrooksBaseball). That may not seem like much, but when you consider that the changeup is only put in play 19% of the time, its pretty significant. Simply put, when batters make contact with the changeup, it’s going to be a grounder more often than not.
Part of that is location.
This is the pitch heatmap for all of the sliders Weaver has thrown this year. The 3 different core locations is a troubling sign, at first. Although it could indicate different approaches to lefties and righties, it could also point toward a lack of command. With Weaver, it indicates different approaches. When you look at the same graphic, but only against right handed hitters, you find something more promising.
This location is, simply put, perfect. The low and away location to righties is a nearly untouchable pitch.
Now, look at the same heatmap, but only against lefties.
This doesn’t seem to be as impressive a location as the previous graphic. But, lefties are hitting just .077 against Weaver’s changeup. In comparison, righties are hitting .250 (BrooksBaseball).
So, Weaver’s changeup is very good against righties, but it is absolutely dominant against lefties. In fact, the young pitcher typically saves his changeup for two-strike counts. He has thrown over half of his changeups with two strikes on the batter. In these situations (any balls, two strikes), hitters whiff about 20% of the time (BrooksBaseball). Not only is the changeup a “worm-killer,” but when he needs it to be, Weaver can use it as strikeout pitch as well.
By working off his consistent fastball, Weaver has developed a plus changeup that has driven his recent success. In his start tonight against the Pirates, watch for the location early. If he is hitting his spots low and away, he’ll be in great shape.