From SABR member Bill Petti at FanGraphs on April 23, 2013:
Earlier this month I wrote about whether we should be concerned with when we see pitchers throwing slower in April, particularly with regards to CC Sabathia.
If we are trying to predict whether the pitcher has truly lost some zip on their fastball, the answer is somewhat. Pitchers who are down at least 1 mph compared to April of the previous year will go on to finish the season down at least 1 mph about 38% of the time. Essentially, they are over four times as likely to be truly losing velocity compared to those that are not down in April. However, the signal gains in strength as the season goes on. So, if a pitcher is down at least 1 mph in July compared to July of the previous year their likelihood of being down at season’s end jumps to 14 times more than pitchers that are not down in July.
Read the full article here: http://www.fangraphs.com/blogs/does-an-april-drop-in-velocity-predict-arm-injuries/
Originally published: April 23, 2013. Last Updated: April 23, 2013.