Over the last week, I took an early look at those pitchers whose fastball velocity has increased most since last season, and those whose velocity has declined. In the comments, several wondered how velocity trended during the season. Intuitively, we would expect that velocity would gradually rise into the summer months as pitchers build their arm strength throughout April and battle through the cooler months. If this is the case, then we would become more optimistic and less panicky about the early season velocity dippers. Let’s see if this happens.
Using the FanGraphs league stats tab, I looked at the average fastball velocity by starting pitchers over the past five years for each month of the season. Below is a table with the data and then a graph to visualize it better.
There are several interesting observations we can make with this data. First is that velocity does indeed increase throughout the season. In the first two years, velocity also continued to rise throughout September and October (when there were actually any regular season games). However, in the most recent three seasons, velocity declined heading into the final month, which does make logical sense.
On average, we can expect a starting pitcher’s velocity to increase 0.6 miles per hour from the beginning until the end of the season. That is pretty significant. Not surprisingly, the biggest jump is from Mar/Apr to May, which represents half the overall increase a pitcher should experience. Of course, for a starter whose velocity is down 2.0-2.5 miles per hour at this point in the season, this impending jump is still not nearly enough to make us feel any better.
Another trend worth pointing out is how fastball velocity has steadily increased every single year. In fact, if you go all the way back to 2002, the first season FanGraphs has velocity data for, it has nearly risen in a straight line. Beginning at 89.5 miles per hour in 2002, average fastball velocity has only declined in two years, while rising in the other eight. Are teams becoming smarter about the importance of velocity and its correlation with strikeouts? I wouldn’t think so, as I would figure teams have always placed significant weight on it.
The data above suggests that pitchers whose fastball velocity is down 0.5 to 1.0 miles per hour should be of little concern at the moment. With an expected bump as the season pushes on, these guys will end up finishing pretty close to where they had been the previous year. However, this also tells us that on average, pitchers do not suddenly regain two miles per hour on their fastball in the middle of the season. This is an ominous sign for aces like Tim Lincecum and Felix Hernandez.