Detroit’s Bullpen Is Churning Out Zeroes

Relief pitching is hard work. More than that, it’s work whose difficulty builds on itself. If you’re covering a single inning in a single game, you can use your best reliever. Second inning? You’ll need your second-best guy, and so on. Second day in a row? Now your best relievers are tired. Third day in a row? Now maybe everyone is tired. And relief work never stops; through Monday’s action, there have been 4,322 starts in baseball this year and 26 complete games.

There’s an inherent tradeoff between how much teams rely on their bullpen and the average quality of the relievers who come in. No one does this anymore, but a team that was only asking its bullpen for a few innings a game could use its best arms for a high proportion of its overall innings. A team full of five-and-dive starters has to go much further down the depth chart; covering four innings per game with relievers requires more contributors.

There’s no obvious correlation between relief innings pitched and quality, for various reasons. Teams aren’t passive observers here; the teams that expect to need more relief innings tend to acquire more relievers, because they know they’ll be needed. Front offices are always on the lookout for innings eaters to lighten the bullpen load. But increasingly, this is just a cost of doing business. Teams and starters are both of the opinion that their best work is done in short bursts. If that’s the case, there will be more relief innings.

You’d have a hard time finding any consistent relationship between relief innings and performance. In 2023, the Giants pitched the most relief innings in baseball and posted the fifth-best FIP-, adjusting for stadium. The A’s pitched the second-most innings… and had the worst FIP-. Philadelphia’s bullpen covered the least innings and was one of the best in the league; Houston’s bullpen covered the second-fewest innings and was below average. There’s a slight positive correlation between innings pitched and ERA-/FIP-, where more innings pitched means higher runs allowed, but it’s quite small.

I mention all of this as a setup for the following fact: The Tigers’ bullpen has pitched more innings than any other unit in baseball this year. They’re 18 innings ahead of the Giants in first place. And that trend is accelerating – Detroit’s relievers have handled 16 more innings than those of second-place Cincinnati in the last month alone.

Some of that is a personnel issue. The Tigers have an ace in Tarik Skubal, but the rest of their rotation is in shambles. Jack Flaherty departed at the trade deadline. Reese Olson hasn’t pitched since July, though he might be back soon. Kenta Maeda got banished to the ‘pen. Those three have made 53 starts for the Tigers; backfilling them has been difficult.

Casey Mize, the team’s current number two starter, has averaged exactly five innings per start this year. Rookie Keider Montero is a rotation mainstay now, but that’s not necessarily a great thing; he hasn’t topped five innings for a month, and his 5.47 ERA and 5.19 FIP mean that the team needs to have relievers ready to cover bulk innings when he gets a start. They’ve been going the opener/bullpen game route quite a bit in the past month; Beau Brieske actually leads the team in starts with six, and he’s pitched 7.2 innings in those appearances.

All told, Tigers starters have averaged 3.5 innings per start in the last month. That’s going to produce huge bullpen output, at least in terms of innings. It’s also almost certainly going to result in some weird lines, like Maeda’s 18.2 innings in five appearances, or Brant Hurter’s five innings per relief appearance average. You could argue that those are displaced starter innings. But regardless of how you look at it, the Tigers have pressed their moderately talented pitchers into service more than anyone else this year, and particularly in the last month.

The wildest part about all of this? It’s working. That tradeoff I mentioned about more pitchers meaning fewer innings for your best pitchers, and thus slightly worse results? It’s not happening here. In this stretch of heavy usage, Detroit’s bullpen has been the best in the majors by a mile. They’ve compiled a 1.92 ERA, comfortably the best in baseball, as well as a 3.21 FIP.

It’s always good to take bullpen stats with a grain of salt. Relievers pitch fewer innings than starters. A few lucky bounces here or there can completely change the top line statistics for an entire season, let alone a month. But that’s not quite as true when we’re talking about a team’s entire relief corps. Their 145.2 innings of aggregate work isn’t so different from a starter’s full seasonal line.

So what are the Tigers doing right? In a word: depth. Detroit has used 13 relievers in the past month. Eight of them have thrown 10 or more innings. Of those eight, seven have produced ERAs and FIPs better than league average. Bryan Sammons is the lone weak link in the group when it comes to recent underlying statistics, and he’s an up-and-down option who isn’t even on the 26-man roster right now. That depth is blunting the cost of heavy bullpen usage. If your fifth guy is about as good as your first, changing their relative appearance rate stings less.

To wit: I think you can make a good argument that the team’s closer isn’t one of their best three relievers going forward. Jason Foley is striking out just 17.3% of opponents while walking 8%, which means plenty of traffic and few free outs. He’s skirted disaster impressively this month, to the tune of a 0.00 ERA in 12 appearances, but I can’t imagine his .154 BABIP against continuing.

Before the trade deadline, Andrew Chafin was the second option out of the bullpen. With him out of town, the Tigers have moved on to Tyler Holton, and here they might have found a gem. His profile is exceedingly strange for a reliever. As David Laurila detailed, he throws six pitches, an unusually deep arsenal for a short-stint bullpen arm. None of his pitches are overwhelming, but he commands them all, and the sheer volume of pitches opponents have to prepare for seems to be serving him well.

The Tigers are also getting Holton in the game at the right times. He’s second on the team in average entry leverage over the past month, behind Foley. In other words, he’s coming in to protect leads or preserve ties. That’s a credit to A.J. Hinch, and also a credit to Holton: He surely didn’t come into the year expecting to be the team’s top setup man, but he’s handling the job with aplomb.

When Foley and Holton aren’t taking the high-leverage innings for Detroit, Shelby Miller is frequently assuming that role. Miller looked like an impact reliever in Los Angeles last year, but the Dodgers didn’t bring him back in free agency. They had a lot going on last winter and not a ton of roster spots, so it’s hardly a surprise, but the Tigers wisely gave Miller a shot on a one-year deal. He’s had a few brutal outings, but he looks like he’s finally hitting his stride; since the start of July, he has an ERA in the mid-3.00s and the peripherals to match it. That’s what you’re hoping for when you sign a pop-up reliever type to a short-term deal.

Is that a dominant top trio? Definitely not. None of Foley, Holton, or Miller is likely to completely shut down opposing offenses. All three are solid relievers, though, and the depth just continues from there. Will Vest is one of four pitchers we list as a “closer” on our Tigers depth chart, and even though we list him fourth, he might be the best of the group going forward. He’s been getting better and better opportunities as the year wears on, and why shouldn’t he? In the past month, only Holton is coming into the game in bigger spots, and Vest is working on two straight years of rewarding Hinch’s confidence in him.

Vest is much less of a weirdo than the other top Detroit relievers. He’s a kind of reliever you’ve seen before, a righty with a fastball/slider combo and a changeup he only breaks out against lefties. There’s no “how is he doing it” here – he’s doing it by striking out 24% of opponents, walking 7%, and keeping the ball on the ground. He’s been back on the Tigers for three years after Seattle briefly claimed him in the Rule 5 draft, and he’s been excellent in that time frame. We’re talking about a 3.33 ERA and 2.97 FIP in 173 innings of work.

Having four pitchers atop the bullpen hierarchy means the Tigers suffer from “closer not available” syndrome less than your average squad. But that doesn’t explain all of their success in relief this year, and particularly this month. Given that they’re handling more than five innings a game, the bulk options in the rest of the ‘pen need to pull their weight as well.

And they largely are. Maeda pitched so badly as a starter – 7.26 ERA, 5.72 FIP, awful ratios – that the Tigers started using him as a bulk guy after openers. Even that experiment didn’t go particularly well, so they pushed him down to a more normal long relief role, where he profiles as roughly league average.

Hurter, on the other hand, is delivering impressive returns when he follows an opener. Whether you consider Hurter a starter or a reliever is really a matter of taste; in the past month, he’s facing 20-ish batters per appearance and going five or so innings. He’s done it once as a starter and five times in the context of a bullpen game, but the general concept remains the same.

I don’t think Hurter is as good as his recent numbers suggest – his Triple-A FIP is a run and a half higher than his major league mark, for example – but I do think he’s a solid swingman, the kind of guy no team would be embarrassed to trot out as a fifth starter. Ty Madden is in a similar boat; he’s up to provide long relief or short starts, and he’s been meaningfully better than his minor league numbers. I don’t think he’s better than league average – but when your third swingman is league average, that’s a good spot to be in.

Pitchers like that are vitally important to competitive teams. Whether you get them via free agency, trade, waiver claims, or internal development, guys who can keep the lights on when your depth chart is challenged by injury and fatigue can be the difference between a bad team and a playoff contender.

This flat bullpen structure isn’t the norm in the majors, but it helps explain Detroit’s ability to cover so many innings and still put up good numbers. They might not have one obvious closer, but they have a ton of reasonable high-leverage arms, so one player’s unavailability never hurts too much. Likewise, they have to cover a lot of long relief innings thanks to their short-starts-and-openers rotation, but they have three acceptable long relievers, so they haven’t run into too many situations where yesterday’s necessity creates a shortfall today.

The true back of the Tigers bullpen is guys like Brenan Hanifee, Ricky Vanasco, Joey Wentz, Sammons, and Sean Guenther. They’re rarely all active at once, but even with all the depth we’ve already discussed, the Tigers need more innings. In this group, I admit that I have no real view on what Detroit is doing right. Those five guys has been downright amazing in the past month – in 45.1 innings, they’ve racked up a 1.99 ERA and 3.27 FIP, though I don’t expect that to continue, as it’s largely down to home run suppression. Still, that group is why Detroit’s bullpen has been the best in the league rather than just a good unit.

To some extent, you have to credit Hinch for putting players in the right spots to succeed. Guenther is best used as a lefty specialist, so that’s exactly how he gets deployed. Sammons can absorb some of those lefties when Guenther isn’t available, though there’s rarely a reason to have both on the active roster at the same time. Hanifee, Vanasco, and Wentz only get low-leverage opportunities. You can’t manage a bullpen throwing 150 innings a month without leaning on every single available reliever, and the Tigers have navigated that dance quite well.

What does this all mean going forward? I wouldn’t focus excessively on any one name here, or any obvious sustainable performance. I’m highlighting Detroit’s bullpen at a local high in performance; they’re closer to league average on the year, with a 95 FIP- and 99 xFIP-. But that’s still a great result! I don’t think anyone came into the year expecting the Tigers to produce an elite bullpen; they were 22nd in our positional power rankings. Putting up top-10 numbers on league-leading volume was definitely not the median outcome here.

The key, as far as I’m concerned, is in casting a wide net and using players interchangeably where appropriate. You can’t put together a bullpen like this if you aren’t hunting for good pitching options all across the board. The Tigers make good use of the waiver wire. They have some minor league free agents contributing. They’ve slotted in demoted starters and promoted minor leaguers who will one day be in the rotation. They’ve even gotten lucky with Rule 5 returns – if the Mariners had kept Vest just slightly longer, he’d surely still be in Seattle given his subsequent performance. Finally, they’ve done a good job developing minor prospects into reasonable contributors.

That’s what I see here: A team that’s well set up to keep producing bullpens that play like more than the sum of their parts. It probably won’t be enough to catapult the Tigers into the playoffs this year – despite racking up the best record in baseball in the past month, they’re three games out of the last Wild Card spot, and we give them only a 10% chance of reaching the postseason.

Even if it doesn’t help them this year, though, this kind of bullpen construction could pay future dividends. The Tigers are going to have better years on the rotation side of things. Their offense is starting to come around. It’s not hard to imagine a good Tigers team headlined by Skubal and Riley Greene, but it’s also not hard to imagine that core coming up short against the top of the AL Central. To succeed in the long run, Detroit needs to surround its stars with great role players. If they continue building their bullpen this adeptly, they’re well on their way to achieving that goal.

All stats are through the games of September 9.