If MLB wants change from the MPH arms race, the modern bullpen must die

Wishful thinking wont protect pitchers from injuries. Rebalancing the sport’s incentives might.

A multi-year report by Major League Baseball was presented to all 30 clubs, including all current managers during the Winter Meetings a week ago. The same data has been reported on subsequently by ESPN, MLB, and other outlets. As Jeff Passan notes, there’s not much we don’t already understand within this data. Pitchers throw harder than ever, spend more time on the injured list for arm issues than ever before, and generally throw both fewer innings per player as well as fewer back-to-back outings for bullpen arms. Moreover, teams have adapted to these issues by working around them in lieu of finding direct solutions. The cascading effect is an ever-growing focus on velocity and spin maximization that is better able to be tracked and refined by increasingly skilled coaches and trainers, and a system that generates exceptional pitching results in the aggregate, at the cost of many individuals. No amount of wishing or finger-wagging will adjust this: the incentive to find and develop pitchers to throw maximum effort exists because it works best. If MLB wants change, they have to rebalance what peak performance looks like.

The league should cut the maximum pitching staff down to 11, or even 10 pitchers.

We had some fun with MLB’s recent rule change discussions here on the site, and I’ll admit I’m not a purist when it comes to sports. I think tinkering is healthy, particularly to allow a game to flourish with multiple viable pathways to success. I liked banning the shift, support the pitch clock, and think hitters should be allowed to break for first on wild pitches to “steal” first. I watch a healthy amount of NPB, Banana Ball, and amateur baseball. I love this sport in all its forms, so do not conflate my aesthetic preference and response to the doomsaying of many within it around this issue as a suggestion that I don’t enjoy it as is. Moss need not grow on a line drive rolling into the right-center gap, as they say.

A key component of this study’s focus was upon the developmental process that has changed to suit modern pitcher usage. In the 1970-80s, teams averaged between 1-2 relievers per game, in an era where league average ERA rested within the 3s every year but 1987. The 1990s brought expansion, steroid use, possibly juiced baseballs, and the first seasons of 2+ bullpen arms per game. By the 2000s, we were consistently seeing just shy of three calls to the pen per side. From the 2010s to today, we’ve crossed that mark, with twin peaks of 3.41 relievers in 2019 and a Covid-influenced 3.44 mark in 2021 that are the full season zeniths for the sport. The introduction of the three-batter minimum after the 2019 season had a mild impact, as the 2024 season was down a hair to 3.26.

This isn’t because pitchers are inherently lesser today, it is because teams have rightly identified the best process to succeed. We have studied the data to understand how much better hitters perform in aggregate against starters the third time through the order – it’s the difference between a mediocre hitter and an All-Star. We know, empirically, that every few ticks of velocity are a massive difference in a pitch’s/pitcher’s effectiveness.

It would be malpractice for anyone in the levers of power of a baseball team to target and develop pitchers without fixating on velocity. Given that the average fastball velocity in 2024 was a record 94.3 mph, a continuing incremental growth now over three mph higher than the 91.1 it was in 2007, this is what teams understand.

Bullpen use is the natural extension of this lesson. 70, 50, and even 20 years ago, when far more starters went 6+ innings per night, many of those pitchers could not hold their velocity and high-effort off-speed over two-thirds of the game or more. Instead, then, asking those pitchers to do more in less time, and cover the rest of the innings with folks who can go 1-2 frames at high effectiveness is being efficient and logical. Arguably just as importantly for MLB organizations, it’s easier and cheaper.

That is to say, no club has cracked how to generate starters who consistently can go 6-8 innings at high degrees of effectiveness with the workload rotations used to carry in eras past. The Seattle Mariners led MLB with 942.2 IP from their starters in 2024. The 2014 Seattle Mariners were 21st in MLB with 952.0 IP. Strikeouts in that period have gone from 19.4% of plate appearances to 22.0%, even with a universal DH. A decade before they were 16.0%, or a jump in K/9 of 6.23 in 2004 to 7.36 in 2014 and now 8.34 per team in 2024. Run scoring has dropped from the heyday of the 90s-00s, but to do so, clubs are employing bullpen-heavy, maximum effort pitching styles that have both an aesthetic detriment and a human cost.

The study from MLB echoes what most recent major research states: throwing at maximum effort is harder on pitchers, and leads to injuries, shorter outings, and shorter careers. There’s nuance, of course, as greater biomechanical efficiency can be a means to minimizing strain. However, the current incentive is what’s been laid out above:

1. Teams understand that the harder a pitcher throws and nastier their off-speed is, the more effective they are at preventing runs.
2. The more effort you put into a pitch, the harder and nastier it has the chance to be.
3. The fewer innings an individual is asked to cover, the more effort they will be able to put into each pitch in those shorter outings.
4. The shorter the outings each pitcher is going, the more pitchers you’ll need on the roster.
5. The more pitchers you have on the roster, the less important any one individual pitcher becomes.
6. The less important any individual pitcher is, the more emphasis you should place on developing as many pitchers to maximize effort as possible and simply churn through them on your roster.

I don’t think it’s necessary to be conspiratorial, given the obvious and evidential nature of this issue, but it’s worth noting briefly that this methodology also benefits organizations over players in MLB’s economic structure, as fewer individuals accrue numbers worthy of recognition through salary arbitration and free agency. A half-dozen relievers each year throwing 20-30 decent innings all add up to league-minimum rates each season in lieu of a single guy racking up 120-150 frames and eventually getting six or seven figures for his durability. But durability is the key word, because that brings us to…

7. The more emphasis placed on maximizing effort in pitchers, the greater that emphasis will be in lower levels of the sport, through the minor leagues on down to college, high school, and youth levels in the U.S. and around the world.

That is the current incentive, and as the study notes, players at every level are responding accordingly. The number of teenagers throwing 95+ continues rising, as do their injury rates. Teams are also being protective of their prospects when they enter the professional levels, in ways that make sense but may not be preparing them for big league work. Increasingly rarely do prospects in the minors work over 5 innings, or throw back-to-back games if they’re relievers. Much like pitch count limits, it’s opaque as to how beneficial they truly are one way or another on a player’s health, but it’s indicative of the greater trend away from emphasizing durability and building stamina against shorter, higher effort appearances.

Like in most areas of the world, much as we might wish that people would do something morally compassionate because many people want it to be so, if people’s financial wellbeing and reputation is incumbent on something, it’s unlikely a system will change. If a GM and manager want to win and retain or improve their jobs, they’ll try to do what works best, for the least cost. If a kid wants to become a big leaguer, they’ll train as hard as they can, focusing on what their coaches and trainers believe will get them seen. If a coach, a parent, an advisor, whomever wants the kid to be a big leaguer, they’ll encourage the kid to build their arm strength and velocity, knowing rightly that it is what teams are looking for most of all. A system like this has no tyrant, it is a diffusion of something few people want on the basis of logic that almost nobody has the means to change.

But almost nobody is not nobody. Rob Manfred, MLB’s 30 ownership groups, and to a lesser extent the MLBPA have the means to alter the only thing that can impact this system: they can change the incentives. If the 26-man roster allows you 13 pitchers, and therefore typically eight relievers, you’d be a fool not to use them. You can use 3-5 pitchers per night, shuttle one or two up and down to the minors or to waivers every week or two, and get by just fine. But a roster with fewer pitchers allowed would mean greater risk to utilizing relievers so cavalierly. MLB recognizes this, and Rob Manfred has spoken intentionally already about utilizing “a few numbers smaller than 13” as early as the 2025 season.

While it would be surprising to see this change instituted at this point for the upcoming season, limits on a descending scale over the next few years are the most natural balm for this challenge. Dropping the limit to 12 in 2025 or 2026 gives clubs the chance to prepare their development strategies, with 11 or 10 coming in the next couple seasons. If you have to suddenly cover more innings with fewer pitchers, you cannot prioritize maximum effort as the holy grail. The Player’s Union fought for a bulwark on this rule as well in the recent CBA, with players going to waivers if optioned more than five times in a single season. Certainly, teams and players will struggle and tinker with what is a reasonable balance, but that is the nature of any change – it highlights unfamiliar change over the rote challenges we’ve become inured to. Stamina and durability will become vastly more prized and, importantly, a focus in development.

That would mean the death of the modern bullpen, yes. However, it would still create immense value in highly effective relief pitchers, as teams would likely need to retain 1-2 max effort pitchers for high-leverage moments. Not every reliever could retain that role, however, and starting pitching that could withstand a third time through, even when dangerous or inadvisable, would return to greater efficacy. There are undoubtedly great adaptations and advantages to be gained, but from a developmental perspective, the ability to demonstrate stamina over pure maximum capacity is a tricky challenge that would be fascinating to watch the sport grapple with more heavily.

This type of roster structuring is also less invasive to the sport’s nature than some other floated ideas, such as a minimum required starter inning total each game, punishing them by losing the DH if they do not adhere. The punishment of a short start in a roster limitation is self-evident: the bullpen is more precious, their innings a resource that must be conserved. From an aesthetic standpoint, this increases the ability for fans to attend or tune in to a game with the foreknowledge that the listed starters will indeed play a primary role in the majority of the game they are looking to attend, something I personally find to be a strong case in favor but recognize is aesthetic taste. Not only do I believe that this change will occur in the near future, but I look forward to it eagerly. The funeral of the modern bullpen, and the birth of something new, exciting, and unknown.