Felix Hernandez and His Fastball, Part 1

(I know I already have another Part 1 out there without resolution, I’ll get to that eventually, but for the moment this has captured my attention)

Near the end of June in 2007, Dave Cameron wrote an open letter to then-Mariners Pitching Coach Rafael Chaves pleading with him to modify the game plan for Felix Hernandez when it came to starting out games. Namely, Dave pointed out the predictability of Felix throwing a high percentage of fastballs at the start of games. A year and a half later and has anything changed? I decided to take a look at Felix’s 2008 through the perspective of Dave’s letter and his intent.

Frankly if you followed any of Felix’s starts and were paying attention (or happened to participate in the game threads at Lookout Landing where I was constantly harping about it), you already know the answer to the posited question above. The answer is no. Now, I could leave it at that, but a 75-word post is not going to get anyone’s attention and besides which, I love making graphs.

Let us jump right into those graphs then. Here is a chart of Felix Hernandez‘s fastball frequency over time; time, for the purposes of a baseball game, being measured in pitches. until it reaches his overall average frequency, about 67%.

If you find a pitch count number along the bottom (x) axis and move upward (y) until you reach the trend line, that value will give you the percentage of pitches, on an average start, that were categorized as fastballs up to that point in the game. So, after 11 pitches, roughly 84% of them had been fastballs. By the time Felix has thrown 40 pitches in a game, that ratio is down to around 74% and it continues to fall

It’s obviously not uniformly descending, but it’s really close and it paints a stark and unmistakable pattern. Felix starts out a game gung-ho about his fastball and slowly begins to work in his other pitches as the game wears on. It’s not even a gentle downward slope, but a rather dramatic curve, suggesting that the set of pitches one through about 20 and 20 through rest of game are rather disparate. Next, we’ll dive a little further into how Felix’s fastball percentage varies on a per pitch basis.

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Matthew Carruth is a software engineer who has been fascinated with baseball statistics since age five. When not dissecting baseball, he is watching hockey or playing soccer.