A few weeks ago, Max Marchi wrote an article for The Hardball Times analyzing pitchers' fastball velocity trends throughout the year. Last year on THT, Josh Kalk developed a preliminary aging curve for fastball velocity. Both Marchi and Kalk used pitchf/x data, which began being recorded reliably back in 2007. I decided to try to more or less replicate their studies, except using Baseball Info Solutions data from FanGraphs.

FanGraphs has monthly splits for all of its offensive and pitching statistics going back to 2002. My sample consisted of just a shade over 2,000 single seasons in which a pitcher recorded fastball velocities in each month. Borrowing the idea from Marchi, I divided a pitcher's monthly velocity by his yearly velocity to come up with a speed index for that month. The average velocity trend looks a lot like a temperature graph.

However, I'm not too concerned about adjusting for the weather. We understand that velocity increases from April to May, but I'm interested in the rate of increase among certain groups of players. I don't know how real these trends are, but for example, Zack Greinke over the last three years has averaged 92 in April and 94 in September. That's a dramatic increase in velocity, so is there something special about him that allows him to pick up steam? On the other hand, Pedro Martinez from 2002-2006 averaged 89.6 MPH on his fastball in April, but actually decreased his velocity as the year went on, averaging 88 MPH in September. Why would he wear down?

I've heard that it takes longer for taller players to find their mechanics, and they therefore throw harder later in the season than they do in April. So I grouped players by height, labeling those at least 6'6" as tall, and those who stand less than six feet as short.

The data seem to weakly support the notion that taller players take a bit more time to reach their velocity than shorter players. I repeated this process with a bunch of different groups of players. Graphs follow.

For girth, I used body mass index, which adjusts for weight by height. Weight recordings are never reliable, so take this for what it's worth.

It looks like heavier players might suffer a bit in the dog days of summer, which makes sense intuitively. Similarly, older pitchers (33 and older) might wear down in the summer months more so than younger pitchers (25 and younger).

And how about a velocity trend based on how hard the pitcher throws? Hard throwers averaged at least 93 miles per hour on their heater for the year while soft tossers were clocked at 88 MPH and below.

There appears to be a large difference in how hard they throw coming out of the gates in April. Or perhaps it's just that faster pitches are more affected by the temperature changes than slower pitches. Many of these groups will correlate with each other, so it could be that the reason tall pitchers start off slow is that they throw hard. Or vice versa.

Finally, I checked to see if velocity trends might be influenced by early workload. I grouped pitchers by those who threw greater than approximately 500 pitches in April, those who threw between approximately 100 and 500, and those who threw fewer than approximately 100.

Might a light pitch count in April pay dividends in August and September?

On to year-to-year trends, also known as aging curves. I tried to copy Kalk's method of using matched pairs and finding the difference in year1's velocity to year2's. My sample consisted of 3,275 matched pairs, with between 100 to 400 pairs in each group. However, unlike Kalk, I do not use a weighted average based on pitch count. I'm not entirely sure that an increased sample of pitches yields a more reliable average fastball velocity. I'm also not sure how to address the selective sampling issues, so for now, I don't.

My conclusions differ from Kalk's. He found that pitchers increase their velocity until they reach age 28 or 29. I find that velocity remains around constant until that age, at which point there is a rather sharp decline in fastball speed. Pitchers who survive in MLB into their thirties tend to lose around two MPH on their fastball.

Again, I'll separate players into groups and come up with aging curves. First by height, with 6'2" as the cutoff.

Strong evidence here that taller pitchers maintain their velocity better than shorter pitchers. How does this bode for Tim Lincecum, who already lost a couple miles per hour of hop on his pitches this year? Before making any assumptions, let's take a look at aging curves by weight class.

Perhaps Lincecum can take solace in the possibility that bulk might be a detriment in aging gracefully.

That's it. Let me know if there are any other types of players who you think might exhibit unusual velocity trends.