Between Mariano Rivera and Trevor Hoffman, there have been plenty of excellent relievers who have anchored a bullpen, and thus are now enshrined in Cooperstown. Conventional wisdom has always placed a high emphasis on having a dominant closing pitcher who can finish off a game, and that remains the case in today’s game. Sure, teams have moved off of valuing the best relievers as closing pitchers, but they continue to pay a high price in free agency for high-end relievers, only to be disappointed repeatedly. In the end, this is illustrating a new hidden truth in the modern MLB- high-end relievers just aren’t valuable, and teams must start configuring their bullpens differently.

A bullpen has been known to be the third most important part of a team’s roster, behind position players and starting pitchers. However, the gap between the three is startling. Between 2016, 2017, 2018, 2019, and ZiPs projections for 2020, here is the amount of Wins Above Replacement (WAR) that comes from each position group:

Position Players: 57.3%

Starting Pitchers: 32.6%

Relief Pitchers: 10.1%

As you can see, a bullpen is worth less than 1/5 of a team’s lineup, and just 1/3 of a starting rotation. However, the gap only gets wider when accounting for the individual player.

Position Player (Divided by 8.5): 6.74%

Starting Pitcher (Divided by 5): 6.52%

Relief Pitcher (Divided by 8): 1.26%

In essence, a relief pitcher is worth about 19% of a starting pitcher or position player, but their current pay doesn’t reflect that. The top of the market for a reliever is Wade Davis’ $17.33 million per year, while the top of the market for position players and starting pitchers is $36 million. That means that the market views relievers as 48% worth what a position player or starting pitcher is, what in reality, the top of the market should be closer to $6.84 million.

Now, one case that fans could point to is that with the increased usage of bullpens, relievers are in higher demand. However, as relievers have been used more often, their performance has consistently regressed:

2019: 18265.2 IP, 4.54 xFIP, 89.2 fWAR

2018: 17428.1 IP, 4.13 xFIP, 102 fWAR

2017: 16469.2 IP, 4.27 xFIP, 112.8 fWAR

2016: 15893.2 IP, 4.10 xFIP, 104.4 fWAR

2015: 15184.1 IP, 3.90 xFIP, 88 fWAR

2014: 14621.2 IP, 3.67 xFIP, 85.2 fWAR

Since teams are still investing so much on high-end relievers, their depth in the bullpen suffers, which is a problem- if relievers are going to be utilized more often, teams must place more of a priority on collecting as many quality relievers as possible. Now, one may wonder if there are potential outliers to this. With that, they should look at the 2018 season.

In 2018, relievers Blake Treinen and Edwin Diaz were fantastic, posting fWARs above 3. In 2019? They combined for an fWAR of negative 0.3. How could this happen? Simply put, Treinen and Diaz illustrate perfectly why you can’t consistently count on one reliever.

Since they pitch under 100 innings, it’s well known that relievers tend to be very volatile in terms of performance. However, the extent of uncertainty teams can have when projecting their production is incredible. Since 2014, there have been 724 instances in which a reliever has pitched 50 innings in back-to-back seasons. Here are is the comparison between the ERA they had in the first year versus the ERA they posted in the second year:

With a coefficient of determination (r-squared) value of just 0.032, only 3.2% of the time could a reliever’s ERA be predicted based on their ERA in the previous season, which is a shockingly low amount. However, this unprecedented amount of instability only increases when you focus on the last few seasons:

2018-2019: Sample- 71, R-Squared: 0.008

2017-2018: Sample- 75, R-Squared: 0.022

2016-2017: Sample- 74, R-Squared: 0.045

As demonstrated above, because relievers have been relied upon more often, the predictable nature of their performance has only gone down. Therefore, teams can never be sure what they’re getting from a reliever, and can’t buy into the fact that “their guy” is an outlier; luck may be the main factor in relief pitcher performance. After all, in a small sample, the “law of averages”, where outcomes tend to balance out over time, is non-applicable, which means that relievers’ home run/fly ball rate, as well as their batting average on balls in play allowed, can change so much from year to year.

Another trap that teams are currently falling into is the idea that they need a strong bullpen to win in the postseason. That not only leads to large contracts for relief pitchers on the open market, but also major mid-season trades when teams believe they are a true World Series contender. However, when examining the past six World Series winners. that may not be the case.

In 2019, the Nationals had the second-worst ERA (5.68), and thus relied on their starting pitchers a lot in the bullpen. Since relievers can get lucky, they were able to muster enough production from their closing pitcher, Daniel Hudson, even though he wasn’t supposed to have that role.

In 2018, the Red Sox ranked 13th in fWAR, but in the postseason, their closer, Craig Kimbrel, struggled to the tune of a 6.92 ERA in 9.2 innings. Therefore, manager Alex Cora asked practically all of his starting pitchers to work out of the bullpen, while ace Chris Sale closed out the World Series for them.

Similarly to the Red Sox, the 2017 Astros had a solid bullpen (8th in fWAR), but their closing pitcher, Ken Giles, was borderline unusable with an 11.74 ERA in 7.2 innings. As a result, he lost hold of the closer role in the World Series, and starting pitchers Lance McCullers Jr. and Charlie Morton finished off Game 7 in the ALCS and World Series, respectively.

The Cubs did not have a productive bullpen in 2016, ranking just 21st in overall fWAR. However, they’re notorious for trading top prospect Gleyber Torres for three months of Aroldis Chapman. Did it work out? Well, Chapman underwhelmed slightly with a 3.45 ERA in 15.2 innings, and blew two saves, including Game 7 of the World Series. Sure, they won the World Series, but it’s certainly not inconceivable to believe they could’ve won it without him; they probably wouldn’t make that trade now.

In 2015, the Royals had a dominant bullpen, ranking in the top-three in fWAR and ERA. Yet, their closing pitcher, Greg Holland, missed the entire postseason after undergoing Tommy John surgery, so their relief corps wasn’t at full strength in the playoffs.

Throughout their three World Series titles, the Giants relied a lot on their starting pitchers to pitch out of the bullpen. There isn’t any better example than 2014, where manager Bruce Bochy trusted Madison Bumgarner to pitch 5 scoreless innings, rather than a bullpen that ranked just 24th in fWAR.

So, if high-end relievers don’t move the needle in the regular season or postseason, how should teams go about building their bullpen? In my opinion, they should use their bullpen as a revolving door, selling relievers at their high point, and buying them on their lows. Take the Tampa Bay Rays, for example. They acquired Emilio Pagan in a small trade from the A’s after he posted a 4.35 ERA, only to watch him dominate with a 2.3 WAR. Rather than hope he could maintain that performance, they traded him for young center field Manuel Margot and catcher prospect Logan Driscoll, each of whom are likely to be more valuable than Pagan. Tampa didn’t value Pagan because they’ve done an excellent job of consistently developing relievers, while they aren’t afraid to take chances  on others as well. Therefore, they have the depth necessary to continuously churn out and adjust to the volatility of relief pitching, which is what every team should strive for.

There are no outliers to this hidden truth; having one high-end reliever just doesn’t matter in today’s game. Not only are they nowhere near worth the same amount of a starting pitcher or position player, but they’re also very difficult to depend on. If teams are going to continue to ask more out of their bullpen, they have no choice but to focus more on building a deep bullpen, which involves buying low on players, while trying to sell high. Their fans may not like it, but the Brewers (Josh Hader), A’s (Liam Hendricks), and Padres (Kirby Yates) should follow the Rays’ blueprint and shop their high-end relievers, who will almost certainly be overvalued on the trade market. It may be hard to acknowledge, but practically every relief pitcher is a replaceable asset, and similarly to running backs in the NFL, teams should not bother to invest heavily in them.