Freaking out about fastball velocity

One of the observations from the opening weekend was that the velocity on Indians pitchers seemed down. This led to some questions and speculation as to why this might be the case. The first thing to note is that Mike Fast had a great piece at the beginning of last season showing that fastball velocity is highly correlated with temperature, and as such, tends to follow a natural curve throughout the course of the season, starting from an early season low-point. That said, a comparison of opening weekend pitch speed to a full-season of data is not really comparing apples to apples. Nevertheless, it is potentially informative to see how the Indians pitchers over the weekend stack up to where they were last season.

Across the board the Indians were low, with the differential ranging from -5.4 (R Perez) to -1.9 (C Perez). The temperatures and early season conditioning probably account for a good deal of the difference, while small sample size and pitch f/x calibration issues possibly filling in much of the remaining gap. In Raffy's case, for example, he only had one pitch classified as a fastball (and possibly questionably so), so I wouldn't put any credence into that number. The broader point is simply that this was an across the board difference, and not something that is strong evidence, by itself, of any individual concern for any given pitcher.