Wei-Yin Chen Has Changed His Style


Chen has altered his profile significantly. Mandatory Credit: Bruce Kluckhohn-USA TODAY Sports

So far this year, the Baltimore Orioles have done pretty well for themselves; heading into tonight’s game against the Brewers, they’re 26-24, good enough for third place in the (surprisingly easy) AL East. Their starting pitching hasn’t really factored into this success, as the rotation ranks 21st in the majors in fWAR. However, one starter has picked up where he left off last season: Wei-Yin Chen, whose 1.0 fWAR in 58.0 innings leads the team.

Looking at conventional statistics, one might be surprised at Chen’s superb fWAR in the early going — after all, his 4.50 ERA doesn’t blow anyone away. By more advanced measures, though, Chen has excelled: His 3.51 xFIP, which puts him at 17th in the American League, more accurately reflects his ability. In 2012 and 2013, he put up xFIPs of 4.34 and 4.14, respectively, so this is obviously a large step forward. In achieving this improvement, Chen has undergone some fairly radical changes:


In his first two years in the league, Chen didn’t accrue many ground balls, but he fanned a decent amount of batters while limiting free passes. This year, he’s giving out fewer walks and strikeouts, but his ground ball rate has spiked. Chen has evolved from a pronounced fly ball pitcher with average strikeout and walk rates to a control wizard with a good amount of grounders to boot. In other words, whereas in his first two years, he looked like a Phil Hughes-type, now he more closely resembles Mark Buehrle.

What’s caused this shift? Breaking his whiff rate down by pitch type, there’s a definite trend for his bread-and-butter pitch:


The four-seam fastball — which Chen has thrown 57.77% of the time for his career, and 55.96% of the time in 2014 — has dropped precipitously in its effectiveness this year; increases by the curveball and the splitter haven’t been able to compensate for it. Contemporaneously, however, the four-seamer has changed its batted profile, as the ground ball rate chart below shows:


While Chen’s curveball, sinker, and slider have all made grounder gains, he hasn’t thrown any of them all that often (the highest rate is the slider, at 12.23% for 2014), and the huge decrease in worm burners from the slider has negated the increase on those three pitches. In the end, his four-seam fastball has driven his change: It doesn’t get as many whiffs as it did in years past, but it compensates for that with a plethora of ground balls — it’s a perfect epitome of Chen as a whole.

So it seems that we can attribute Chen’s new persona to the four-seamer. To what can we attribute that pitch’s evolution? It’s not much faster than before — he’s currently averaging 93.0 miles per hour on it, compared to an average of 92.3 over the preceding two years. Any changes, therefore, would most likely come as the result of different pitch location.

Brooks Baseball tracks all pitches thrown, and includes — among many other statistics — the locations in each section of the strike zone. If we divide the zone into three horizontal sections, the impetus behind this new Chen becomes clear:


In 2014, Chen has still relied on the four-seamer, but not in the same way as years past. He’s now eschewing the high fastball more than in 2013 and 2012; while this has probably cost him many swinging strikes (and, ergo, quite a few strikeouts), it’s also boosted his ground ball rate considerably. Basically, Chen has pitched lower in the zone with the fastball, and this sole change has, ostensibly, led to his impressive 2014.

Wei-Yin Chen achieved modest success in his rookie and sophomore campaigns, but he’s taking his game to the next level this year (at least, in terms of peripherals). Change can be a curse or a blessing, and in the case of Chen, it certainly appears to be the latter.

All data courtesy of FanGraphs and Brooks Baseball.