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…
