Are Returning Pitchers Throwing Harder?

As you might imagine, I watch a lot of baseball for work, and one of the things that stands out to me the most this year is just how dang hard pitchers are throwing. I’m not just talking about that new hotshot reliever your team called up who’s dropping triple digits like peak Aroldis Chapman, though that’s part of it. I’m talking about existing starters, guys I’ve watched for years, adding a little oomph.
Max Fried has topped out over 100 mph this year; his teammate Kyle Wright has never thrown harder. Framber Valdez is up nearly two ticks on average. Carlos Rodón already threw hard, and now he throws even harder. You can’t walk 10 feet without tripping over a pitcher throwing harder than ever – or so it seems to me, a fairly interested observer.
But appearances can be deceiving. I can think of any number of baseball truths that were considered evidently true by observation for years, only to later be disproven. I decided to put my eyes to the test. Have pitchers learned how to throw harder from one year to the next, changing the fundamental truth of how aging works? Let’s find out.
My method is fairly simple. I took every starter who threw at least 10 innings since pitch-level data began in 2008. I took their average four-seam fastball velocity, but only in games they started; I didn’t want to have swingmen who changed roles within or between seasons in my data. From there, I looked at every pitcher to see if he’d thrown in the majors the previous year, and if so, the change in fastball velocity from one year to the next.
In this way, I got a yearly sample of how much every returning pitcher in baseball’s velocity changed, on average, every year. As a quick example, there were 176 pitchers who compiled at least 10 innings as a starter in both 2013 and ’14. On average, they threw 0.21 mph slower in 2014 than they did in ’13. I found those pairs for every year, which gave me a yearly average of velocity changes over time. Read the rest of this entry »