We'll spend one quick paragraph covering off on the basics. Coke's ERA is pushing ten this season after last night's struggles. His WHIP is a shockingly high 2.09. His FIP and xFIP aren't horrible somewhat surprisingly, coming in at 4.97 and 4.96, respectively, but those numbers don't exactly scream reliable reliever, and that's the best news Coke has to rely on right now.
Where are Coke's problems most noticeable? Unfortunately, there's not a single area to pinpoint.For starters, his velocity is down. His four seam average according to PITCHf/x is just 91.3 MPH, when he's traditionally been around 93 MPH, with the 2011 season being the exception, when the Tigers tried to make Coke a starter. And it's just not the point where he's sitting with his velocity is down, but his max velocity is down too. Each of the last four years, he was topping out in the 97-98 MPH range, but in 2014, he hasn't topped 95.
Unsurprisingly, that's resulted in a reduced number of swing and misses. His four seam fastball, which traditionally missed bats around 8% of the time (not a great percentage mind you), is down to 3%. His two seamer isn't any better, missing bats just 3% of the time.
When a fastball becomes less dangerous, it usually goes hand-in-hand that his off-speed pitches can lose their effectiveness, too. If a player at-bat isn't worried about Coke's ability to throw his breaking ball for a strike, he waits for the fastball. If the fastball velocity isn't what it once was, the difference between the fastball and the changeup become less.
In this case, both appear to be issues. Coke's changeup has traditionally been 10 MPH slower than his four seam fastball, a typical velocity differential between the two pitches. This season, again per PITCHf/x, there's only about a 7 MPH differential. That may not seem like much in the grand scheme of things when we're talking about pitches in the 80-100 MPH range, but for a big league hitter, when the two pitches come in at a similar speed, there's less to be fooled by, and a higher likelihood of hitting the pitch. And after missing 27% of bats with his changeup last year, and 22% the year before, he's only getting a swing-and-miss 10% of the time.
Coke also historically relied on his somewhat loopy, somewhat biting, breaking pitch (you can call it a curve, a slider, or a slurve, it's the same pitch). He threw it about 25% of the time, and would get a whiff anywhere from 15-20% of the time. This season, at a slightly lower but still similar usage, he hasn't generated one swing-and-miss with his breaking pitch.
But as a left-hander, perhaps Coke can still be utilized as a left-handed specialist? It's a nice thought, but so far this season, his wOBA against left-handers is actually worse than right-handers, at .466 vs. .459. In a similar number of batters faced, he doesn't have any more strikeouts, or any substantial difference in results when splitting out his performance between the sides of the plate. He is getting a few more swings and misses against lefties, at about 9%, but that's still below the 12-15% range he's traditionally been in. And when you zoom in on only the pitches a batter swings at, he's missing the bat about 17% of the time against lefties – that was 25% last year, and 30% the year before.
This isn't meant to take anything away from Coke's accomplishments for the Tigers over the years. He's been a reliable reliever for years in filling multiple roles for the club, inspired a popular Twitter handle (The infamous Phil Coke's Brain), and will forever exist in Tigers GIF lore for his glove spike after they beat the Yankees in 2012 in the ALCS (Phil Coke glove spike!). But the reality is, Coke isn't that pitcher anymore, and doesn't appear to be a fit for any role in a bullpen with World Series aspirations.
This may not be the end of Phil Coke's career. A number of these issues mentioned above are fixable (improving the breaking pitch, dropping the velocity on his changeup). But it's probably time that it's the end of him with the Tigers.
Note: Data referenced in this analysis comes from Pitch INFO at BrooksBaseball.net and PITCHf/x at FanGraphs.com.