Investigating Wei-Yin Chen's Early Season Velocity

Wei-Yin Chen isn't a flamethrower. But he does throw slightly harder than the average major league starting pitcher. A pitcher's velocity certainly isn't everything, though it's worth keeping an eye on. And in his first start, Chen's fastball speeds were below his career averages and could possibly be an indication of the reversal of a recent trend.

Since entering the majors in 2012, Chen has an average velocity of 92.5 mph on his four-seam fastball and 91.9 mph with his sinker (or two-seam fastball). In 4-1/3 innings on Tuesday, Chen averaged 91 mph on his four-seamer and 90.1 mph on his sinker. By itself, that doesn't mean much; we're only talking about a few dozen pitches in his first appearance of 2015.

Let's take a look at Chen's average fastball velocities from April in his three previous seasons:

Date	FF	FT
Apr. '12	91.0	90.7
Apr. '13	92.0	90.5
Apr. '14	93.0	92.6

Chen has only ever pitched in three major league games where one of his fastballs averaged below 90 mph: on April 28, 2012; May 20, 2012; and April 26, 2013. So all occurred relatively early in the season.

In his first two seasons, Chen started out the year with lower fastball velocities. But that wasn't the case in 2014, and that improved velocity propelled Chen to his best season as a major leaguer. Chen has actually thrown his fastball harder every season in the majors (his age 26-28 seasons):

It's been nearly a decade since Chen had Tommy John surgery (in 2006), and he's throwing harder now than he has in a long time (and maybe ever). While pitching in Japan for the Chunichi Dragons, Chen's fastball velocity had actually been in decline before joining the Orioles:

2009: 90.7
2010: 90.2
2011: 88.8 (possible leg injury)

Pitchers usually don't see a consistent fastball velocity uptick in their late 20s. But whatever Chen has been doing now that he's in the majors has been working. Perhaps that includes a more disciplined workout regime, better coaching and guidance, and, except for an oblique injury in 2013, pretty good health (no arm injuries, at least).

Interestingly enough, Chen mostly throws fastballs, but he's starting to trade four-seamers for more sinkers:

He hasn't had to trade fastballs for more offspeed pitches; maybe that's something that will happen when he starts to lose velocity. But even if the gradual change in fastball usage hasn't had a dramatic effect, Chen's HR/9 dropped from 2012-2014 (1.35, to 1.12, to 1.11), and his flyball percentage has also dipped in the same span (42.1%, to 41.1%, to 37.5%). Chen's groundball percentage hasn't followed suit, exactly (37.1%, to 34.4%, to 41%), but last season was his career best in that department. Chen is not transforming into a groundball specialist or anything close to one, but it'll be intriguing to see what happens if he continues to opt for more sinkers.

Chen has previously demonstrated that a start or two with lower than average velocity (for him) doesn't mean bad things are necessarily on the horizon. But at some point his velocity is going to stop climbing and will level off and start to decline. As an impending free agent, Chen could be playing for another team before that becomes a real concern. But as the Orioles' lone lefty in the rotation, Chen bears a different kind of responsibility, and the O's would surely welcome a rebound effort in his next start.

Photo via Keith Allison