Strip away all the data — traditional, analytical, and everything in between — and one number stands as the best barometer of J.T. Realmuto’s value in free agency.

525.

That’s how many games Realmuto, late of the Phillies, has started behind the plate since the outset of 2016, fewer than only St. Louis Cardinals icon Yadier Molina (545). Realmuto has caught 4,590 innings in that span, also second to Molina (4,638⅓). If not for a late-season hip injury that sidelined him for 11 games, Realmuto likely would lead that category.

“Part of his value is the volume of games he can play in a season,” one National League executive said this week. “His greatest asset is his durability.”

But will that durability endure? Realmuto turns 30 in March. Can he hold up as well over the next four or five years as he did over the last four or five?

The Phillies and every other team that is interested in Realmuto are asking that question. Because everyone understands the price tag. Arguably the valedictorian of this free-agent class, Realmuto wants to raise the bar for catchers, which means beating Joe Mauer’s $23 million annual salary from 2011 to 2018. It will take big money, be it $23.5 million per year, $25 million, or more, to win this bidding.

The real risk is the length of the agreement. History shows that catchers tend to age poorly. This might not be Realmuto’s last contract, but it will be his largest, so he will seek at least four years, maybe five or six. And with most of his value tied to his work behind the plate, teams want to feel comfortable that he can keep catching for the bulk of the deal.

“I think the greatest concern is the wear and tear of the position and the impact over time on the productivity of the player,” former New York Mets general manager Steve Phillips said recently. “What’s a catcher going to look like at age 35? What are his legs going to be like? What’s his ability going to be like? The analytics say they could decline, and it could happen quickly.”

Fangraphs valued Realmuto at a total of 15 wins above replacement from 2017 to 2019 and 1.7 in the 60-game 2020 season. Twenty-one catchers all-time were worth at least 17 WAR from ages 26 to 29, according to Fangraphs, but only 10 achieved that level between 30 and 33.

Part of the reason catchers rarely retain their value into their 30s is that many wind up changing positions. Only 47 catchers have gotten 500 or more plate appearances while playing at least 75% of their games behind the plate in their age-30 season, according to Baseball-Reference.com. That group whittles to 41 catchers at age 31, 29 at age 32, 18 at age 33, 19 at age 34, and 12 at age 35.

It’s relevant because Realmuto’s offensive production must be viewed through the prism of his position. Over the last four seasons, he slashed .276/.335/.477 for an .812 OPS, far superior to the average catcher (.238/.310/.397, .707 OPS). But his numbers don’t stand out as much compared to the average first baseman (.257/.338/.462, .800 OPS) or designated hitter (.243/.322/.435, .757 OPS).

When the Twins signed Joe Mauer to an eight-year, $184 million contract extension in 2010, he was the best catcher in baseball. But he had to stop catching later in his career because of injuries.
JIM MONE / Associated Press
When the Twins signed Joe Mauer to an eight-year, $184 million contract extension in 2010, he was the best catcher in baseball. But he had to stop catching later in his career because of injuries.

The Minnesota Twins saw that with Mauer. From 2008 to 2010 (ages 25 to 27), he averaged 116 starts behind the plate, finished in the top 10 in MVP voting three times (winning it in 2009), and racked up 12.4 WAR. But after his eight-year, $184 million extension took effect in 2011, he never caught more than 75 games in a season because of injuries and compiled 18.3 WAR through 2018.

Likewise, Buster Posey averaged 7.6 WAR per year from 2012 to 2016, when he started 111, 119, 109, 103, and 122 games as a catcher. Beginning in 2017, his age-30 season and four years into a nine-year, $167 million extension, the San Francisco Giants gave him more time at first base. Since then, Posey has averaged 92 starts at catcher and, not coincidentally, 2.9 WAR.

Phillips, who hosts a show on SiriusXM MLB Network Radio, faced a decision on signing Mike Piazza to a long-term contract in 1998. Like Realmuto, Piazza was entering his 30-year-old season, and the Mets understood what happens to most catchers in their 30s. But Piazza was a Hall of Fame-caliber hitter, so they took a chance, figuring they could move him to first base and still get elite production.

It worked out. Piazza not only slashed .289/.367/.534 for a .901 OPS and averaged 28 homers per season over the seven-year, $91 million contract. He also started 135, 124, 127, and 119 games behind the plate in the first four years of the deal.

Looking back, though, Phillips had reservations.

“When your catcher is such an important part of your offense —— your 3-hole hitter or your 2-hole hitter — when he’s taking a day off, your offense is much different. You’re not nearly as good an offensive team,” Phillips said. “It’s a challenge to build your team with a high-level offensive catcher because 20 to 25 percent of the season you’re taking a big cog out of your offense.”

That would be mitigated if the National League permanently adopts the designated hitter. But although the owners and players seem to favor the universal DH, it might have to wait until the collective bargaining agreement is renegotiated after next season.

Former Phillies catcher Darren Daulton is an example of a backstop who continued to play well in his early 30s.
Jerry Lodriguss / Staff Photographer
Former Phillies catcher Darren Daulton is an example of a backstop who continued to play well in his early 30s.

Regardless, there are examples of ageless catchers. Jorge Posada, Ivan Rodriguez, and Molina stayed behind the plate and sustained their offensive production well into their 30s. Russell Martin was better from ages 30 to 33 (.762 OPS in 2,008 plate appearances) than 26 to 29 (.701 OPS in 1,936 plate appearances).

The Phillies have had several catchers who aged well, notably Darren Daulton (.869 OPS and 17.1 WAR in 1,918 plate appearances from ages 30 to 33) and late-blooming Carlos Ruiz (.829 OPS and 12.4 WAR in 1,705 plate appearances from 30 to 33).

Maybe Realmuto’s career will follow that arc. Maybe it won’t. Either way, the team that signs him will likely have to make that four- or five-year bet.

“It seems like catchers who are a little bit smaller in size, which Realmuto [at 6-foot-1] is, are probably a little bit safer back there,” Phillips said. “He’s athletic. He can run. There’s got to be an acceptance that he’s going to be the highest-paid catcher on an [average annual value] basis. The issue comes down to how many years, and you understand the risk involved.”