The Impact of Fastball Velocity on HR/9
Personally, I find that the complexities of pitching make it the most interesting part of baseball. Many aspects of pitching go in to achieving success, and one aspect is limiting home runs. A pitcher’s effectiveness at limiting home runs can be easily measured by using HR/9, or the number of home runs a pitcher gives up per nine innings. (The league average HR/9 is around 1.0 each season.) Here, I examined how a pitcher’s fastball velocity affects their home run rate. Before I started, I expected to see a velocity threshold that a pitcher must meet to achieve an above average HR/9, and I expected a big difference in HR/9 for those who do not reach the threshold.
To do this, the process was simple. Using data for pitchers who had over 160 innings pitched in each season between 2006-2013, I generated a FanGraphs table that included the pitcher’s name, the year, their average fastball velocity, and their HR/9. I then created an aggregate table, breaking velocity up in to simple ranges.
To do this, the process was simple. Using data for pitchers who had over 160 innings pitched in each season between 2006-2013, I generated a FanGraphs table that included the pitcher’s name, the year, their average fastball velocity, and their HR/9. I then created an aggregate table, breaking velocity up in to simple ranges.
From this table, a line graph can easily be created.
The first thing that stood out was that there was not the sharp decrease in HR/9 that I had expected. The graph suggests that, as a generalization, a player should have an average fastball velocity above 91.0 mph to have a league average HR/9, and to have a truly elite HR/9 (around .85), a pitcher should be throwing fastballs at least 93.0 mph. Of course, there are many other effects that impact a pitcher’s HR/9 rate, but velocity can be used as a rough guide in larger sample size, especially as a predictive tool for pitchers entering the twilight of their career.
A great example of using fastball velocity to predict home run rates is with Dan Haren. Haren was once an elite pitcher for the Angels and Diamondbacks, but his production has trailed off since. As shown in the following table, Haren limited home runs reasonably well from 2005-2008 (In 2003 and 2004, Haren only pitched portions of seasons, so the statistics have not had time to stabilize and thus are not reliable). In each of these seasons, his fastball velocity was above 91.0 mph. However, during the seasons between 2009-2013, his fastball velocity dropped below 91.0 mph, and his home run rate suffered. While his HR/9 is at a career low so far in 2014, it is because he has not pitched nearly enough innings for it to stabilize. His fastball velocity is also at a career low, so his HR/9 should correct itself over the course of the season, decreasing Haren’s overall effectiveness.
A great example of using fastball velocity to predict home run rates is with Dan Haren. Haren was once an elite pitcher for the Angels and Diamondbacks, but his production has trailed off since. As shown in the following table, Haren limited home runs reasonably well from 2005-2008 (In 2003 and 2004, Haren only pitched portions of seasons, so the statistics have not had time to stabilize and thus are not reliable). In each of these seasons, his fastball velocity was above 91.0 mph. However, during the seasons between 2009-2013, his fastball velocity dropped below 91.0 mph, and his home run rate suffered. While his HR/9 is at a career low so far in 2014, it is because he has not pitched nearly enough innings for it to stabilize. His fastball velocity is also at a career low, so his HR/9 should correct itself over the course of the season, decreasing Haren’s overall effectiveness.
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