Tyler Glasnow‘s fastball in his last start had some glove side movement to it, looking like a cutter. Despite the way the pitch looked, his fastball is a fourseam and not a cutter.
In his start against the Boston Red Sox, Tyler Glasnow’s fastball featured some glove side movement, especially when he throwing it up in the low 90s. This 92 mile per hour fastball that caused a Blake Swihart groundout had some glove side break to it, other pitches in the game had more pronounced movement to them. Compare that to this harder fastball that Glasnow used to strike out Xander Bogarts. The fastball getting the groundout broke more glove side, compared to the more “rising” fastball Glasnow got on his strikeout. So perhaps Glasnow added a new pitch to get more swinging strikes? The swing and miss stuff in the minors has only translated to a 19.5 percent strikeout rate and 9.1 percent swing and miss rate for Glasnow. But that perceived new pitch looks to be just perceived.
Baseball Savant publicly shares the statcast data, so getting all cutters thrown in a game this season and all of Glasnow’s fourseam fastballs is rather easy to obtain. The two labels for pitch movement are Pfx_Z for the vertical movement and Pfx_X for the horizontal movement, all from a catchers point of view with units in feet. 0.0 horizontal movement represents a straight pitch, and the vertical movement is compared to a pitch with no break.
Taking Glasnow’s fourseams and plotting them with the reference lines at 0.0 on the axes shows:
Glasnow’s heater has some movement to the plus side of 0.00, which would be considered glove side movement, so the ball cutting that way is real no surprise. His ball has that tail to it with his fourseam grip. Having just his fastball movement doesn’t bring in any story other than it has cut action, so here is Glasnow’s fastball movement overlaid on the movement of all right-handed pitchers cutters:
Glasnow’s fastball has less vertical and glove side movement than the rest of the cutters, but it could be just a bad cutter as there were cutters with similar movement as Glasnow’s fourseam, but the bulk of the cutters have more movement glove side.
Looking at the average pitch movement of the cutters and Glasnow’s fourseam shows:
|Pitch Type||Average Pfx_X||Greater than 0%|
The average right handed pitcher cutter broke 0.1267 feet glove side, and 66.77% had greater than 0.0 feet of glove side movement. Glasnow’s fourseam averaged -0.4203 feet of movement, or 0.4203 feet of arm side movement, and about 10 percent of his fastball’s had plus glove side movement. Glasnow’s fastball also had the 14th lowest arm side movement of right-handed starters with 200+ fourseams thrown according to Baseball Prospectus’ PitchFX leaderboards. The perception of the pitch looking like a cutter isn’t really all that surprising.
The data does show that Glasnow’s fourseam has some cut to it, but that’s not the only reason to think he’s not adding the cutter. This is likely more important than any data on the pitch, as Glasnow is the one holding the seams of the ball and throwing the pitch, and he denies throwing a cutter, telling Matt Gajtka of Pirates Prospects after the start last Sunday that:
"“My fastball cuts, usually,” he said. “Thirty percent of the time, 40 percent of the time, it has a natural cut to it, so that’s always kinda … that’s how I’ve always pitched.”Second, he shrugged off the variance in speed as unintentional.“That’s just going down the mound a little quick,” Glasnow explained. “It gets ‘behind’ me.”"
Glasnow’s always had the velocity, but the cut action might have been lost due to the results he has produced so far, focusing attenion more on his control issues than pitch action. The data has shown that Glasnow’s ball does cut at times, he has one of the lowest arm side movement on his fourseam fastball, and Glasnow mentioned that he has natural cut on the pitch. The pitch is a fourseam and not a cutter, but the way it moved and looked against the Red Sox might be a sign Glasnow is figuring out how to use his fourseam to get outs at the big league level.