Relievers Are No Caged Birds and No Net Ensnares Them

Kamil Krzaczynski-USA TODAY Sports

Some birds make great pets. My great Uncle Bob and Aunt Marge had a green parrot named Stanley. (I’m using the past tense since Marge and Bob have passed on, but Stanley may very well still be alive, since Amazon parrots can live long enough to collect social security.) This particular parrot could make a noise that sounded just like the ringer on Bob and Marge’s landline telephone. He said “Bob” in the exact intonation that Marge used when calling across the house to her husband. And while Stanley could be a bit of a chatterbox, when they pulled the cover over his cage for the night, he quickly quieted down until morning. Stanley epitomized (epitomizes?) repetition, consistency, and longevity.

Relievers are not like Stanley. Relievers, particularly good ones, are rare and exotic birds, with comparatively short lifespans. They prove tough to even spot, much less capture and domesticate. Bird watchers go to all sorts of extreme measures to finally hear the song of a Bewick’s wren, or spot the scarlet tanager that eludes them despite living in its native land. Meanwhile GMs and Presidents of Baseball Operations (POBOs) employ all sorts of strategies to bring in quality relievers. But try as they might, the phantom late-inning aces ignore their calls.

Because of the inherent volatility of relief pitchers, decision-makers must build their bullpens using small tidbits of information gleaned from observation. In their dreams, POBOs compile collections of lights-out closers, but in the real world, the goal is to gather a flock of average or better performers who compile innings. Thus, moving forward, this article will define a productive or “good” reliever season as one where the pitcher throws at least 40 innings and posts an ERA- of 100 or lower.

So how rare are these productive birds and how long do they sing? Among over 2,300 relief pitchers who are no longer active, but debuted this millennium, 604 posted at least one productive season (as defined above). Looking at the careers of just those 604 relievers, they turned in on average 2.5 good seasons, with 76% logging three or fewer good seasons, 84% logging four or fewer good seasons, and 90% logging five or fewer good seasons. Quality relievers are hard to find and even harder to keep. They grace our visage for a short time before disappearing above the treetops.

To add more detail to the arc of a reliever’s career, I constructed something akin to an aging curve, but one that’s heavily modified to account for the fact that relievers are a bunch of weirdos who don’t fit cleanly into any structured system. Because pitchers shift to relief at different points in their career progression, using a set age range on the x-axis doesn’t make sense for this use case. Instead, this career curve centers around each pitcher’s peak season, i.e. of their seasons with at least 40 IP, the one with the lowest ERA-. Non-peak seasons were assigned an index relative to the peak year, which is indexed as 0. So if a pitcher peaked in 2009, his 2008 season would be indexed as -1 and 2010 receives an index of 1. The y-axis will track ERA- since it’s already nicely scaled for this purpose. With those changes accounted for, the remainder of the curve’s creation follows the methodology proposed by Jonathan Judge back in 2020, which uses a Generalized Additive Model, rather than the traditional delta method:

It shouldn’t be too surprising that the curve looks a little woozy. Instead of depicting a rapid rise followed by a small plateau, and a gentle decline as with most aging curves, the reliever career curve goes not as the crow flies, but as the carrion bird scavenges. The typical path starts with a couple years of respectability before hitting that peak (which since we’re dealing with a minus-stat, is visually depicted as a dive, but this time it’s a good thing!), then hitting a rough skid. Since this curve was constructed as a quick one-off, no adjustments were made to account for survivorship bias, so those who stick in the league for more than a couple years start to take over the average, which explains the tick up in performance three-ish years after that peak season.

To look at the lifetime of a reliever from one more vantage point, after posting two productive seasons, relief pitchers are typically good for around 2 WAR over the rest of their career, which might be clustered within a couple of really solid seasons, or scattered across several seasons dotted with a combination of injuries and periods of ineffectiveness. Or in terms of WPA, after a second good season, relievers on average accrue 1.5 points of win probability, which in a best-case scenario is one stellar season, but might also wind up as several seasons of mediocre to poor performance.

None of this is meant to imply that relievers aren’t valuable. Rather it illustrates that their value is super concentrated and difficult to time. The nature of relief pitchers and their career arcs make acquisitions of any kind a tricky task for a POBO, but in this article, I’d like to use the information amassed above to pick apart the process behind a few deadline reliever trades. Trades centered around relievers sometimes seem counterintuitive (insert more gesturing at the fleeting and unpredictable nature of relievers here). Tracing the logic behind a reliever trade can be a bit like tracking a painted bunting that hasn’t developed its colorful plumage yet. That said, reliever trades provide a somewhat unique opportunity for two teams that both fancy themselves contenders to trade with one another rather than needing to match up with a team mid-rebuild.

The Mariners have shown up to two separate trade deadlines as contenders and provided blueprints on how to trade a reliever with double-digit saves in the first half. In 2021, they traded Kendall Graveman and his 10 saves to the Astros. This past July, they traded Paul Sewald and his 21 saves to the Diamondbacks. In both cases, the Mariners received big league talent that created depth at positions of need (Joe Smith and Abraham Toro for Graveman and Rafael Montero; Josh Rojas, Dominic Canzone, and minor leaguer Ryan Bliss for Sewald).

In the short-term context of the season in question, both trades did what they were designed to do: shuffle production from one part of the roster to another. However, trading a late-inning reliever at the deadline tends to represent the waving of a white flag; these moves rankled both fans and the players still left in Seattle’s clubhouse. The confusion was warranted. The trades did feel weird. And despite running this play a couple of times now, the Mariners still haven’t mastered the messaging to their employees or fans. (And while we’re here, I’ll note that any perceived praise of these trades in isolation should not be viewed as an endorsement of Dipoto’s recent comments on his .540 winning percentage philosophy, as that’s a much larger conversation about both the validity of the strategy and whether it needs to be spoken about in public.)

But if we can get past how weird it feels for a contending team to trade a high-leverage reliever, perhaps a useful strategy lurks in the undergrowth. In both scenarios, Seattle had one or more relief pitchers in the bullpen ready to step in and close out games – Drew Steckenrider and Sewald in 2021 and Andrés Muñoz this season. The Mariners also boast an affinity for developing pitchers in-house, which earns them a “there’s always more where that came from” type of confidence when trading good pitching.

Meanwhile, what we know about the typical career arc of a relief pitcher makes it unlikely that a team will experience seller’s remorse even though it might feel bad in the moment. When Seattle traded Sewald, he was in the midst of his third productive season, already beyond what most relievers manage. Hopefully, he turns in several more strong seasons, but the Mariners needn’t feel foolish for not counting on it. Graveman was only in his first strong year as a reliever, but given that he started for so many years prior, he’s a particularly odd case.

A valuable player of the type that’s always in demand at the deadline combined with the confidence that other players within the organization can step in and take over that player’s role in the bullpen sets the trade machine in motion. After that, the risk analysis is the same as any trade. Is the return large enough? Does it satisfy a positional need? Are the prospects on the desired timeline to contribute to the big league club? Since contending teams trading quality relievers don’t necessarily need to make this move, they own more leverage than a team out of the race looking to get any return at all on an expiring contract. Contending teams can wait for the right return, which doesn’t just mean the best players. These trades can take on the feel of a single-season fantasy football trade, where teams trade from areas of strength to shore up weaknesses. Or a team that feels set for the current season can use this as an opportunity to start planning for the future by acquiring prospects or big leaguers with extra years of control left on their contracts.

The Graveman and Sewald trades actually happened, but what about one that didn’t? Veteran closer Kenley Jansen finished 42 games for the Red Sox in 2023 and earned 29 saves along the way. He posted an 80 ERA- over 44.2 IP, a super solid season. But Chris Martin, Josh Winckowski, and Brennan Bernardino all bested Jansen’s ERA- and threw more innings. Jansen’s track record earned him the closer’s role, but Boston clearly had viable in-house options to replace him and room for improving their current roster and future outlook. Maybe they explored trades and the right return never materialized, but in retrospect it feels like a missed opportunity.

On the other side of the ledger, teams looking to acquire a late-inning reliever work through a different calculus. Teams trying to win right this very second lack the luxury of time to develop from within or pick up a project pitcher on the waiver wire. That strong reliever on a team with reasonable replacements holds more value to a team with a thin bullpen. As strange as it sounds when speaking about numbers and hard production, not all WAR is created equal. The WAR that pushes a team from being a game or two back into a playoff position is worth more than WAR that extends a comfy division lead. Likewise, future value has zero value to a team that needs to win today. Teams valuing the same player differently doesn’t always imply that one is right and the other is wrong. Sometimes it means the two teams find themselves in different situations.

Consequently, reliever trades sometimes look lopsided when evaluated in a vacuum, but in context, acquiring backend bullpen help doesn’t mean overpaying despite everything discussed above about the sustainability of relief pitchers. Consider the decision to order delivery for dinner rather than cooking at home. Does delivery cost more? Yes. Does that make it an overpay? Not necessarily. Time is valuable and the time saved on cooking can be reinvested in other tasks. Depending on the specific circumstances, cooking may take longer than ordering something, and minutes are precious when hanger is threatening to destroy all of your close relationships. If a team has been fasting from postseason appearances and finds itself in the heat of a playoff race, it makes sense to check the wait times and prices to get a pizza in the building before things get any more dire.

Though perhaps the confounding optics of this type of a trade prevent them from happening too frequently, the 2022 trade deadline served up a few examples. Minnesota acquired Jorge López from Baltimore to provide some added stability to their middling bullpen; they sent the O’s a trio of prospects alongside Yennier Cano. The Orioles rested on the brink of contention at that point, but saw an opportunity to add a few more bulbs to an already bright future. Atlanta sent Will Smith to Houston for Jake Odorizzi as an example of teams aligning their complementary strengths and weaknesses. And finally, Milwaukee traded Josh Hader to San Diego for a combination of immediate and future contributors in Robert Gasser, Dinelson Lamet, Taylor Rogers, and Esteury Ruiz.

Though relievers simply refuse to be normal and conform to the expectations of managers and front offices, decision-makers needn’t throw their hands up in exasperation. Rather, embrace the weird. Understand that the reliever lifespan is closer to the two to five year life expectancy of button quail than it is to the 15-20 year life expectancy of a cockatiel. Treat those productive years as the transient treasures they are and be prepared to go to great lengths to enjoy that concentrated value. POBOs have the opportunity to take their own inspiration from the uncaged birds and extend their lifespans to that of a Stellar’s sea eagle (the sturdiest of all eagles), by allowing relievers and their fierce, independent spirits to go with the wind. Thus freeing us all from the rigid conventions of deadline reliever trades.





Kiri lives in the PNW while contributing part-time to FanGraphs and working full-time as a data scientist. She spent 5 years working as an analyst for multiple MLB organizations. You can find her on Twitter @technical_K0.

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Ivan_Grushenkomember
6 months ago

The Sewald trade was criticised on FG comments as trading a useful reliever for replacement level parts, not the idea of trading a useful reliever in the first place