A while ago I looked at the success of a changeup based on its speed separation from the preceding fastball. Since then I had the pleasure of answering some of Dave Cameron's questions on the Mariners. He asked me about Felix Hernandez's changeup, which keeps getting faster.

At the same time his fastball has actually slowed slightly, so that the separation between the two pitches has gotten smaller. The difference averaged 9mph in 2007 and is down to 5mph this year. My work suggests that on a pitch by-pitch basis a separation between 5 mph and 10 mph is optimal, while others showed that on an overall average basis the bigger separation the better. Either of these results would suggest that Hernandez's changeup should be getting worse every year. But that is not he case. Remember that the run value is the change in run expectancy so negative is good for Hernandez.

+-------+------------------+-----------------+
| Year  | Changeup Run Val |  Aver CH/FB Dif |
+-------+------------------+-----------------+
| 2007  |           -0.017 |         9.0 mph |
| 2008  |           -0.022 |         7.1 mph |
| 2009  |           -0.032 |         5.2 mph |
+-------+------------------+-----------------+

At this point Hernandez's changeup is amazing, one of the top few in the game. It is interesting that his success runs counter to the prevailing trend. To examine it further I plotted the run value of his changeup based on its speed.

Overall felix's changeup gets better with increasing speed, which is very unlike the average player's changeup. As most pitcher's changeups get faster they start looking just like slow fastballs and get crushed, but since Hernandez throws such a fast changeup he can succeed throwing as his changeup fast as some pitchers throw their fastballs. Next I wanted to check out the success of his changeup based on how much slower it was than the preceding fastball.

Where as for the average pitcher there is a plateau in which the changeup is equally successful between 5 and 10 mph slower than the preceding fastball for Hernandez success peaks at 5 mph and falls off rapidly if it gets any slower. This again shows the Hernandez is succeeding with a fast changeup.

There are important limitations to studies that show trends for all pitchers averaged together; all pitchers are different. In this case Felix Hernandez succeeds with a power change that has little separation from his fastball. That same separation for the average pitcher, with a slower fastball, would be big trouble.