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Mike Fiers: Spin Doctor

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Seattle Mariners v Oakland Athletics
Like a man on fire, Mike Fiers has been dominant in his time with Oakland.
Photo by Thearon W. Henderson/Getty Images

The story started with the Oakland A’s offense being the central figure. Then the bullpen took center stage. Finally it’s the starting rotation’s turn to play hero with the recently acquired Mike Fiers being a primary factor.

Fiers was having a fine season with Detroit prior to his trade in early August. But since then he’s been excellent, throwing 18.1 innings with a sub-2 ERA and 21 strikeouts. His FIP and xFIP, while higher than his ERA, agree that he has been quite good for the A’s. His high-strikeout, low-walk results have much to do with that, I’m sure. Fiers is enjoying career-best results in those areas. I think his four seam fastball is to blame.

Fiers has thrown nearly 850 four seam fastballs this season, equaling 40 percent of his pitches, according to Statcast. While 40 percent is up from 32 percent last season, Fiers had generally thrown fastballs 50-60 percent of the time in his career. The 2305 revolutions-per-minute Fiers has averaged on fastballs this season is the highest spin rate of his career, however.

A quick refresher on Spin Rate reminds us that the higher the spin rate, the better the pitch:

“As more data have become available, most experts have agreed that fastballs and breaking balls are tougher to hit when they possess higher Spin Rates. In fact, some data suggest that Spin Rate correlates more closely than Velocity to swinging-strike percentage.”

So now we know that Fiers has increased his fastball usage of late, and he’s also increased his spin rate, which is believed to be a skill. Do the results match up? As a whole, yes.

Fiers’ Four Seam Fastball by Year

Year # % MPH BA XBA SLG XSLG WOBA XWOBA EV LA Spin BB% K% Whiff%
Year # % MPH BA XBA SLG XSLG WOBA XWOBA EV LA Spin BB% K% Whiff%
2018 843 39.7 89.1 0.225 0.238 0.429 0.507 0.302 0.343 90.6 24 2305 6 21.2 19.9
2017 861 32.7 89.5 0.272 0.256 0.544 0.517 0.390 0.379 89.6 23 2258 13.5 27 22.8
2016 1205 43.5 90.1 0.341 0.309 0.651 0.563 0.432 0.392 91.1 20 2188 7.2 16.2 19
2015 1762 58.3 90 0.251 0.246 0.438 0.435 0.327 0.326 88.7 20 2186 8.4 22.7 19
BaseballSavant.com

It is also true when you split his season between his time with Detroit and Oakland.

Fiers’ Four Seam Fastball by Team: 2018

2018 Team Pitch % BA ISO BABIP SLG wOBA xwOBA xBA Spin Rate Velocity
2018 Team Pitch % BA ISO BABIP SLG wOBA xwOBA xBA Spin Rate Velocity
Detroit 39.3 0.229 0.205 0.248 0.433 0.308 0.345 0.234 2299 88.9
Oakland 42.6 0.190 0.190 0.250 0.381 0.240 0.317 0.276 2347 90.1
BaseballSavant.com

Whatever Fiers is doing to increase his spin rate is working as he hasn’t enjoyed this much success since his days in Milwaukee. In 56 starts with the Brewers from 2011 to 2015 Fiers posted a 3.66 ERA/3.61 FIP/3.67 xFIP line and more than a strikeout per inning. A common thread through Fiers’ best years is the presence of catcher Jonathan Lucroy, who played with Fiers in Milwaukee the entire time he was there.

Fiers was already enjoying a successful campaign with Detroit and has shown flashes of dominance before, so his run with Oakland isn’t totally unprecedented. The difference in his spin rate is something to monitor, however, and may be evidence that this isn’t just a hot streak.