What would Yankees legend Mariano Rivera be worth as a free agent?

It’s Hall of Fame time once again, and while I couldn’t care less about the institution itself, this year’s ballot is among the best in its history. At the top of the ticket is the greatest relief pitcher of all time, and my personal favorite player growing up, Mariano Rivera. You all know his story and his stats, so I’m not going to get into them here. One of the more fascinating things about Mo, to me, is the impact he had on relief pitchers in general.

Modern bullpens are used as a game shortener. Managers know they only need to get to the seventh inning or so with a lead, and the likes of Josh Hader, Dellin Betances and Jordan Hicks will bring home the win. It’s a far cry from the old firemen roles, or the even earlier relief corps that would simply come in to staunch the bleeding the rare times a starter didn’t finish a game.

Mariano was the best in baseball history at shortening games and it’s hard to quantify just how much easier he made the lives of Joe Torre and Joe Girardi. When your ninth inning will be pitched by a man with a 205 ERA+, it’s one less high-stress, high-risk call you have to make. This leads to a very obvious question, given the new value seen in relief pitching: What the heck would the best reliever ever get on the open market?

Like the rest of this series, I ran a Play Index for the most similar pitchers to Mo, who under today’s CBA would have become a free agent in 2001, after his age 31 season. The trouble with this is largely the structural shift in reliever usage. Rivera sports the second best bWAR of a reliever ever, but that misses the per-inning dominance that modern closers boast because they don’t pitch quite as many innings. Remember, Rivera’s best season by WAR was his setup year in 1997, just because he threw so much more.

So with that in mind, it’s better to evaluate Rivera against his own kind, the elite closers who have signed big free agent deals.

If you ever needed proof that pitchers are better than ever, and wondered why batters strike out so much more, just look at this table. Compared to the best closers of today, Rivera is...fine. He’s right around the average for adjusted ERA, but well below the average for K-BB%. He’s just not as dominant on a per inning basis as an Aroldis Chapman or Kenley Jansen.

Of course, free agency is more complicated than just two stats. Relievers especially enjoy a “postseason premium”, since they can be leveraged in October to contribute more than starters or batters. Rivera was ludicrously good in the postseason, and reliably so. We all remember watching Chapman and Jansen be worn down by their respective managers right before hitting free agency, and it helped them cash in big. Imagine what that attitude would do for a man who was coming off four straight World Series appearances.

I’m not sure what winning a ring is worth for a reliever. Chapman and Jansen both signed massive deals after the 2016 season, but only Aroldis was a World Series champion. Jonathan Papelbon had a World Series ring as well, but it was a couple of years before becoming a free agent. Craig Kimbrel of course just won a championship with the Red Sox, and it’s yet to be seen how that will affect his market rate. At the very least, Mo owning four rings before hitting free agency would have added a bit to his contract value.

The other unknown element in a hypothetical Rivera free agency is his longevity. Relievers, by and large, burn bright and then flame out. They are the most volatile, hardest to predict position group, and that propensity to crater in their early to mid 30s is why I’m so bearish on the Yankees pursuing Andrew Miller, David Robertson or Zach Britton this offseason. Bullpen arms just don’t have great track records for sticking around.

Mariano, of course, is the most hilarious exception to that rule, pitching at an elite level until his 40s. In fact, you can do the math yourself. In his first seven seasons, he had a 182 ERA+. He retired with a career 205 ERA+. Mo got better, and considerably so, in his thirties!

It’d be really hard for a team to know that ahead of time, and therefore would be tough to bake into any projected free agency contract. You can probably say Rivera would settle in around the Kenley Jansen deal — five years for $80 million. He’d get credit for such a stellar postseason track record, but he’d be dinged for being a little older and not quite as elite on a per-inning basis as the best in the modern game.

So we’re talking pretty casually about giving Rivera the second largest contract for a reliever in history, and all I can think of is what great value that would be. Mo just got better and better as time went on, and assuming his career played out the same way, with him lasting as long as he did, I don’t think anyone would balk at that valuation. He’d be worth every penny.

Mariano Rivera will waltz into the Hall of Fame on the strength of his credentials. But he deserves a spot as a builder, a contributor to the modern game. He was a failed starter who became immortal working out of the bullpen. The Jansens and Kimbrels of the baseball world owe him for changing the way we see relievers. Today’s best closers are probably better, inning per inning, than Rivera. But they stand on his shoulders, the shoulders of a historical, if not literal, giant. He showed 30 franchises the value of having someone shorten your game. I don’t know about you, but five years and $80 million seems like a bargain for that.