18 June 2015

Wei-Yin Chen's Hot Streak and Velocity Improvement Later in Seasons

For most major-league pitchers, velocity is everything. The loss of one mile-per-hour on a hurler's fastball can punch his ticket to the minors, or an uptick of the same degree can elevate him to stardom. Pitchers therefore want to maximize this, obviously, and avoid any stretches of poor performance in this regard.

During the first five starts of the 2015 season, Wei-Yin Chen struggled significantly. He struck out only 16.8% of the batters he faced, walked 9.2%, and allowed fly balls on 48.8% of his balls in play — an unsavory combination that gave him a 132 xFIP- for those 28.2 innings. Since then, though, he's done a 180; posting a 24.5% strikeout rate, 3.9% walk rate, and 38.4% fly ball rate, he's brought his xFIP- down to 80.

An impressive turnaround, that — and one whose cause isn't hard to discern:

Fourseam Twoseam Slider Curveball Changeup
Velocity, 4/7/15-5/3/15 90.3 89.7 81.3 72.3 81.9
Velocity, 5/9/15-6/15/15 91.5 91.2 82.6 72.9 82.3

More velo = better results. Case closed! Chen's velocity should stay high, and the good times will continue to roll.

But wait. The early part of the season still happened. Might this same thing, and the mediocre play it brings, occur in the years to come?

Let's look to the past. In 2012, Chen's first season stateside, he experienced the same initial slump, albeit a bit more extended:

Fourseam Twoseam Slider Curveball Changeup
Velocity, 4/10/12-6/1/12 90.2 89.5 81.1 72 83.1
Velocity, 6/6/12-10/1/12 91.4 90.4 80.4 71.7 84.6

Like in 2015, he became more powerful in late summer and fall, and performed better with that clout (102 xFIP-) than without it (112 xFIP-). And moreover, the same thing transpired the following year:

Fourseam Twoseam Slider Curveball Changeup
Velocity, 4/3/13-4/26/13 90.5 89.9 81.6 70.5 83.1
Velocity, 5/1/13-9/28/13 91.8 90.7 81.4 72.9 83.8

His April xFIP- of 130 overshadowed by a 97 xFIP- from then forward, Chen didn't look back after some early hard times.

So Chen has always packed on more velocity in the later parts of the season? Not necessarily: His 2014 campaign saw him post consistent velocity — and output — throughout. If the Orioles bring him back for 2016, will that stability reappear, or will Chen once again fare poorly at the year's start?

There's no singular, definitively correct reason for Chen's 2014 season. Oddly enough, Chen had to rehab from a knee surgery in the offseason that preceded it — the only time he's recuperated before the year starts. The extra work he put in on that may have driven up his April and May velocity. Plus, for what it's worth, he vowed after 2013 concluded that he'd "come back stronger" the next year.

Then again, most pitchers don't throw as hard when the year is still young, usually on account of rust from inactivity and colder weather. Knowing nothing else about Chen, we'd probably expect him to lose some velocity at first; knowing that he's done so in three of his four MLB seasons, we'd definitely expect the same.

As with most pitchers, velocity gives Chen success when present, and robs him of it when absent. He currently finds himself with as much stuff as ever, to his benefit; however, come the start of 2016, he might lose some of that, and could see some bumps in the road as a result. Every player strives for consistency, but despite his efforts, Chen may not attain it.

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