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April 14, 2014

Moonshot

Does April Velocity Last?

by Robert Arthur


This early in the season, when the samples sizes are small and the conclusions fragile, attention tends to focus most especially on pitch velocity. That’s a reasonable thing to do, since velocity stabilizes quickly. Because velocity is the simple result of the acceleration a pitcher can impart to his pitch, it is not as affected by luck as, say, batting average or ERA (or even the advanced metrics like tAV or FIP). Moreover, velocity is of prime importance in predicting a pitcher’s future success.

Velocity is deceptively simple. It is only a single number, and yet it can explain multitudes about a pitcher: the kind of pitches he throws, how he gets hitters out, and in aggregate, the kind of pitcher he is. I set out to explore the early-season changes in velocity, and to what extent they are predictive of the season’s velocity.

I ought to note up front that this analysis is well-trodden ground. However, there is room for exploration and improvement. It’s a new year, and so there’s a new crop of April data to be mined for potential velocity breakouts (and breakdowns).

The Consistency of Velocity
Perhaps the most striking feature of velocity (besides its obvious implications for pitcher performance) is how consistent it is between seasons. Here are 118 pitchers’ median fastball velocities from 2012 and 2013, plotted against each other. For the remainder of the analysis, I’ll limit myself to starters in 2013, attempting to predict their velocities for 2014.

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Related Content:  Velocity

8 comments have been left for this article. (Click to hide comments)

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evo34

Some feedback: can you reduce the number of decimal places in your tables from eight to, say, two? Hard to read as is.

Also, what was the actual formula you came up with to convert last year velo. and current year velo. to predicted rest-of-season velo.? Thanks.

Apr 14, 2014 05:58 AM
rating: 3
 
BP staff member Ben Lindbergh
BP staff

Number of decimal places reduced.

Apr 14, 2014 07:31 AM
 
BP staff member Robert Arthur
BP staff

Thanks for the feedback.
in terms of the model, the equation is...
Velocity in full year = .97 * velocity in previous year + .56 * (April [this year] velocity - April [of previous year] velocity) + intercept (2.8, in this case)

So, the difference in April velocities is worth roughly 1/2 as much as the previous year's velocity.

Apr 14, 2014 14:00 PM
 
BillPetti

Good article. I looked into this in a related way at FanGraphs back in 2012 (http://www.fangraphs.com/blogs/at-what-point-should-we-worry-about-velocity-loss/). I found that April velocity had a correlation of .931 with rest of year velocity, which was good but a few ticks less than later months. I didn't include previous year's velocity, which is an add I like here.

Also, comparing velocity in the same year and month a year ago gave some interesting hints as to whether a pitcher would experience a true velocity loss or gain (http://www.fangraphs.com/blogs/when-is-velocity-gain-likely-real/) in the current season. April was predictably the least telling of the months, but begin down or up in April compared to the same time a year ago does give you some increased information.

Apr 14, 2014 09:09 AM
rating: 1
 
BP staff member Robert Arthur
BP staff

Thanks! I should have linked to your articles, they are nicely complementary.

Apr 14, 2014 11:22 AM
 
jwise224

I'm surprised Brandon McCarthy wasn't noted as a "riser" given that his sinker is up two miles per hour this spring compared to the pitch's average velocity in 2013. Is this due to his 2012 and 2013 data, which dropped the predicted 2014 velocity? If so, I'm curious how 2012 performance is weighted compared to current 2014 performance and which set of data is more telling going forward.

Excellent work and thanks for sharing!

Apr 14, 2014 09:35 AM
rating: 0
 
BP staff member Robert Arthur
BP staff

McCarthy juuuust missed the list: he's right after Dillon Gee, with about a .5 mph predicted increase. He's also shifted his pitch usage a lot, which is intriguing.

To clarify, though, I only included the 2013 velocity in the model. I could also bring in data from earlier pitcher seasons, but didn't for this particular analysis. I suspect it would prove largely redundant with the 2013 data (given how consistent velocity usually is year-to-year), but it might contribute a small increase in predictive power.

Apr 14, 2014 11:29 AM
 
Pat Folz

I remember KG and Parks talking about how the Orioles (and some nonspecified other franchises I believe) just "didn't like" the cutter as a pitch, because they were afraid of 1)developing bad habits in young players but also 2)they were afraid it would slow the arm down, or lead to lost strength, or something. I didn't quite understand the reasoning but that's stuck with me, and the declines of Harrell's and Shields' stuff raises an eyebrow.

I also note that the splitter is frequently considered an "old person" pitch (in that prospects rarely have one before reaching the majors), and that Buchholz is losing velo on his other fastballs as he uses it more. Might be (probably is) nothing more than connecting two random dots on my part... but then again, it might not be. It's something to watch going forward I think.

Apr 14, 2014 18:56 PM
rating: 0
 
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