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October 29, 2009

Checking the Numbers

Quick Change Artistry

by Eric Seidman

Were you to take a web journey to a search engine and query the terms "fastball, changeup, sequence," a slew of sites would surface, many of which include in their brief synopses that a sequence of this sort helps keep hitters off balance. Conventional wisdom dictates that these two pitches, when thrown one after the other, can fool a hitter based on their similar movement and vast velocity gap.

As we have discussed over the last few weeks, velocity is not always as advertised, since several factors dealing predominantly with the reaction time of the hitter can either speed up or slow down the perception of pitch speed. Pitchers that utilize a cambio are usually judged on the velocity discrepancy relative to their heater, but such judgments can prove inaccurate if and when the hitters perceive the velocities to be closer in value than the radar gun suggests. It then stands to reason that the ultimate goal in evaluating fastball/changeup sequences involves measuring the perceived velocity of the off-speed offering to the perceived velocity of el numero uno, given that perception matters most.

Both Josh Kalk—now an analyst with the Tampa Bay Rays—and Dave Allen, of Baseball Analysts and FanGraphs, have already done some great work in this area. Back in February, Kalk examined the run values of each two-pitch sequence, finding that a changeup on the heels of a heater benefited hitters to the tune of 0.02 runs per 100 pitches. Hitters were not necessarily world-beaters off of this sequence, but they clearly held an advantage over those making the deliveries. One reason might be that pitchers, as a whole, were not optimizing their perceived velocity discrepancy between the two pitches. Another could be that those with higher success rates simply were not using the specific sequence as frequently as those without. In a separate study, he also found a positive correlation between the success of a changeup and the difference between the seasonal velocities for both pitches; the greater the difference, the more likely success would be observed.

Allen tackled the issue in a slightly different manner, evaluating the success of a changeup based on the speed separation from the previous fastball in each plate appearance. The results surprisingly suggested that there was little difference between success rates when the changeup ranged from 5-12 percent slower than the preceding fastball. The results were non-linear, with slight alterations within that range but rapid drop-offs on each side. They also conflicted with Kalk’s findings, as one study suggested that changeups five miles per hour slower than a pitcher’s average fastball were less successful than those 10 mph slower, while the other indicated little difference between 5-10 mph separations. One potential reason for this, mentioned in the comments of Allen’s thread, tied back to absolute velocity of pitches; a 95 mph pitch may work well with an 84 mph changeup, but the same 12 percent drop applied to an 89 mph heater would produce a 78 mph pitch that hitters might find easier to time and tame.

What happens if we apply these ideas to the world of perceived velocity? Might the picture become a bit clearer? After all, throwing a down-and-away fastball followed by an up-and-in changeup is going to increase the risk that the second, slower pitch gets hit hard, based on the crossover effect. Regardless of the gap between the velocities pitchers average according to radar gun readings, we would expect that pitchers with lower perceived deltas will afford hitters more opportunities to hit the ball hard. Harder-hit balls will translate into more bad outcomes for pitchers. In other words, for now, forget about the absolute difference between a fastball and changeup, and instead focus on the percentage of how much slower a changeup is perceived to be in relation to the perception of the immediately preceding fastball in the same at-bat.