The A’s occupy one of the AL’s two wild-card slots, and the other day they picked up Mike Fiers. They’re about to use him out of the rotation. I tried — I promise — to come up with some kind of Mike Fiers article, but I couldn’t do it. I didn’t think it would be interesting. The A’s added a below-average starter, but, into the rotation he goes. That might be the real story here, how the A’s have gotten where they are despite a patchwork rotation that no one expected. The A’s have given Brett Anderson nine turns. They’ve given Edwin Jackson — literally Edwin Jackson — eight turns. Fiers probably will help, if only for the fact that he can reliably pitch. The group he’s joining appears paper-thin.

Which isn’t to suggest that I don’t think much of Sean Manaea. Manaea, at least, has been a familiar constant. But there’s a surprise in here, too, a guy without whom the A’s would be struggling. Contact rate measures bat-to-ball contact per swing attempt. The lower the contact rate, the better a pitcher is at generating whiffs. I looked at every starter this year with at least 50 innings. The guy with the lowest contact rate allowed is Chris Sale. In second is Patrick Corbin. In third is Max Scherzer. In fourth is Trevor Cahill. The A’s signed Cahill for $1.5 million in the middle of March, seemingly as a response to losing Jharel Cotton. Cahill’s started 13 times, and he’s ended up an absolute bargain.

If I wanted to make some kind of unconvincing point, I could just say that Cahill has been a far better investment than Yu Darvish. But, better than that, Cahill presently ranks third in WAR among free-agent starters. He’s behind Miles Mikolas, but he’s also thrown half as many innings. And then he’s behind Jake Arrieta, but Arrieta, too, has pitched a lot more often. Durability is a factor here, and Cahill has twice been on the disabled list — once for a minor elbow thing, and once for an Achilles thing. But you know I’m a sucker for rate stats, and rate stats are where 2018 Cahill shines. Behold his percentile rankings among starters in various significant categories:

By park-adjusted ERA, he’s just outside the top 10%. By park-adjusted FIP, he’s just outside the top 10%. By park-adjusted xFIP, he’s just outside the top 10%, and by wOBA allowed, he’s just outside the top 10%. I threw in ground-ball rate just to add some variety; it’s not quite as important as the others, but Cahill is a ground-ball pitcher like few other starters. It’s one of the factors behind his success.

I know that percentile rankings are one thing, and you can see from that plot that Cahill’s been good. About how good has he been, though? Another way to illustrate this is by listing off some names of comparable pitchers. So, using ERA-, FIP-, xFIP-, and wOBA, here are Cahill’s ten closest 2018 comps to date:

Obviously, that’s a tremendous assortment of pitchers. That table includes some of the best pitchers in baseball. I’m not trying to pressure you into believing that Trevor Cahill is therefore one of the best pitchers in baseball, but the numbers are what the numbers are. With many analytical articles, the point isn’t so much the statistics themselves. It’s the general story the statistics are telling. With Cahill, the story is that he’s been a quality starter, when he’s been able to start. The market was down on him, as evidenced by the terms and the timing of his contact, but for the Oakland rotation, Cahill has filled a void. He’s given them something behind Manaea to allow the unit to remain respectable.

I’ve referred to Cahill in here as a surprise. Without question, he’s exceeded just about everyone’s expectations. And yet, in his defense, this performance hasn’t come completely out of nowhere. I remember writing about Cahill a couple times last season, when he was pitching for the Padres, and then when he was traded to the Royals. After Cahill went to Kansas City, he had some shoulder problems, and his season went off the rails. But in the following table, you’ll see how he did as a starter in San Diego. The lines are almost identical.

Trevor Cahill, Starting Pitcher Year Team IP Pit/GS K-BB% ERA- FIP- xFIP- GB% Contact% 2017 Padres 61 94 18% 89 80 78 57% 71% 2018 Athletics 75 91 18% 75 79 78 55% 69%

Basically, the A’s version of Cahill is exactly like the Padres version of Cahill. Same strikeouts, same walks, same grounders, same everything, more or less. Because 2017 Cahill got hurt and got worse, his strong start was almost forgotten. And, in fairness, it’s not always the smartest thing to do to rely on pitchers coming off injury-riddled seasons. But the A’s rolled the dice on the idea that Cahill’s shoulder might be back or close to 100%. If the shoulder was responsible for how his performance dropped off, perhaps a healthy shoulder would allow for a repeat of that strong initial performance again. I don’t know how confident the A’s were about that taking place, but so far it’s worked out. If we can’t really predict injuries, I suppose, that means, in a way, we can’t really predict health. Trevor Cahill has been healthy enough to play a major role for baseball’s 2018 Cinderella.

As one more point that’s loosely related, recall that Cahill is a ground-ball machine. The A’s were hoping for health more than anything else, but they’ve also inserted Cahill into a supportive environment. Here’s how every team in baseball has done against ground balls, in terms of wOBA allowed:

The A’s are in first, in large part because of Matt Chapman. They knew before the year they’d have Chapman and Matt Olson handling the corners. The A’s assumed they’d have a good infield defense, and the evidence validates the assumption. The infield works to Cahill’s advantage. His strikeouts take care of most of the rest.

There are two takeaways here, I guess. The first is that, in retrospect, Cahill looks like a hell of a signing. He has a full repertoire, he came into the year healthy, and before he was hurt a year ago, he was terrific. The A’s now look smart for taking the chance. The second takeaway is that, like last year, this could come to a sudden, screeching halt. The strongest indicator of future injury is past injury, and Cahill’s record isn’t clean. He could get hurt again, and it could ruin the rest of his season. It’s already happened once, in recent memory, and this is part of the reason why adding Fiers makes sense, as unexciting as that is. Fiers is better than Oakland’s depth options, and those depth options might’ve become important. Fiers is insurance, because the Oakland rotation isn’t stable.

For right now, though, Cahill is one of several roster bright spots. For as long as he’s able to pitch, it looks as if he’s truly become an above-average starter. No, he’s not the kind of guy who’ll reliably pitch into the seventh or eighth. But that’s not really what baseball’s asking of starters anymore. Especially for a team with Oakland’s bullpen.