To set the stage, this discussion of Justin Verlander will be focused solely on the velocity of his four seam fastball so far this season, and compare that to prior years. Data referenced will include PITCHF/x data from FanGraphs and PITCH INFO data from Brooks Baseball.
So, to kick things off, Verlander's velocity is down. His average fastball velocity sits at 93.3 this year, and 94.7 last year according to FanGraphs. Brooks Baseball shows a similar but slightly larger gap, at 95.1 in 2012 and 92.8 in 2013.
This isn't just a case of Verlander "starting slow," as has been the conventional wisdom on him of the time. In April 2012, he sat at 94.4, and in May, he was up to 94.8. At an average of 95.1, it stands to reason a bump in his velocity will come as the summer months set in, but those April and May averages still reflect a noticeably higher average than his current 2013 showing.
Should we be worried? Well, let's dig in deeper.
First off, are the averages a fair representation? In fewer games, variance in performance can increase. Extracting individual game data and averaging it (note: this isn't perfect as it doesn't measure each pitch equally, but rather, each game equally, but is an adequate representation), Verlander's average velocity was 94.4. And coincidentally, his median velocity was 94.4 as well. On the other hand, using the same eight game sample, his 2013 performance results in a 93.0 average, and a 93.3 median.
This data helps identify a bit of an outlier in 2013; Verlander's first game of the year, a frigid day in Minnesota, in which his average velocity came in at just 91.6. Conversely, Verlander does have one game stand out in 2012 as well, his complete game against Kansas City, in which he maxed out at over 100, and averaged nearly 96 miles per hour. Remove those two odd ball games, and Verlander's differential becomes 94.2 in 2012, and 93.2 in 2013.
So, there's still a gap, but not quite as large as it initially appeared. We have yet to see Verlander pull back and hit triple digits on the gun, but that doesn't mean he won't get there sometime this year when the situation calls for it, and punishing an average because of a game played in near-freezing temperatures also doesn't make much sense.
Speaking of the weather; that has to impact things too, right? Especially after such terrible weather to start the season. Well, yes it does. When the game time temperature is colder, Verlander's average velocity drops. Scatter plotting these 16 starts over two years, a very clear trend line emerges. The trend line shows a nearly two degree swing in average velocity based on the temperature, ranging from 35 degrees up to 70 degrees.
But, the data doesn't show a dramatic difference between the two seasons. The average temperature for his starts in 2012 came in at 55.3 through eight starts, and 2013 was identical at 55.3.
When we differentiate between the 2012 and 2013 starts, it becomes clear this isn't some fluke driven by poor temperatures. With 2012 shaded in blue and 2013 in red, on similar temperature days, the blue or 2012 season almost always beats out the red 2013 MPH. In fact, his best velocity game this season (Saturday's performance against Cleveland) at 93.9 MPH was on average faster than only two of Verlander's eight starts to this point last year.
What does this all mean exactly? Well, while not extrapolating too much or taking too much of a leap, it does likely mean that Justin Verlander is in fact human. His fastball, while still powerful, doesn't pack quite the same punch it did in 2012, or any of the prior three seasons, either.
This doesn't mean Verlander will become a less effective pitcher, or that he's pitching injured or anything along those lines. But, weather, outliers and all others removed, Verlander's velo just isn't quite what it used to be.