The induction this weekend of Scott Rolen into the Baseball Hall of Fame and Adrian Beltre residing in the on-deck circle, waiting only to find out if he receives the largest share of the vote for a third baseman upon earning election on the first ballot next year, has again brought to the forefront one of the questions most frequently asked by Cooperstown scholars and observers:

Why is it so difficult for third basemen — only 18 of whom are enshrined in the Hall of Fame, the fewest of any position — to crack the Cooperstown code?

The answer may have been pictured on a laptop inside the visitor’s dugout at Citi Field last month.

“Mike Schmidt,” said Cardinals star Nolan Arenado, no worse than the second-active third baseman, as he looked at the list of all-time WAR leaders at the hot corner. “My goodness gracious.”

Schmidt, who leads the position in WAR at 106.8, is an imposing enough standard. But those directly behind him — Eddie Mathews, Beltre, Wade Boggs, George Brett and Chipper Jones, all of whom finished with a WAR of 85.0 or higher — have all combined to raise the bar for Arenado and everyone else to begin marching down a Hall of Fame path at third base.

The only other position whose top six all-time players have a WAR of 85 or better is right field, which was the home of Babe Ruth and Henry Aaron, the first two men to reach 700 homers, as well as Stan Musial, Mel Ott, Frank Robinson, Roberto Clemente and Al Kaline.

But unlike right field and most positions on the diamond, third base has traditionally demanded its elite performers excel on offense as well as defense while displaying durability.

“Because you’re closer to the batter, there may be a more mental toughness than (there) is being farther way from the ball,” said Mets bench coach Eric Chavez who won six straight Gold Gloves at third base for the Athletics from 2001-06 before his career was derailed by back and shoulder injuries. “At times I felt like a hockey goalie. I kind of took on that mentality of I was going to lock in and stay in front of it.”

The seventh-best third baseman per WAR is Brooks Robinson, who racked up 39.1 in defensive WAR, the third-most in history behind only shortstops Ozzie Smith and Mark Belanger.

“I’ve always seen third base as an integral defensive position on the field,” Rolen said during a conference call last week.

Coincidentally, the eighth-best third baseman per WAR is Paul Molitor, who made 44 percent of his appearances at designated hitter and polished off his Hall of Fame resume by hitting .316 with an OPS+ of 123 and 1,449 of his 3,319 hits while playing zero innings at third base from 1991 through 1998.

The top eight third basemen in WAR averaged 2,619 games, or more than 16 full 162-game seasons. Padres star Manny Machado and Arenado, who rank 22nd and 23rd all-time in WAR among third basemen and debuted within eight months of each other in 2012 and 2013, have played 1,525 and 1,476 games, respectively.

“I think the one thing, when we see those guys and what they did, is the longevity,” Arenado said as he continued looking at the WAR leaderboard. “Mike Schmidt played for a very long time — probably longer than I’m going to want to play for, to be honest with you. Eighteen years, that’s something. Beltre, Mathews — 21 (years), 17, Chipper, 19.

“Got to give them credit because they stayed healthy. They deserve to be in the Hall of Fame because of that longevity and being able to stay consistent throughout that longevity.”

But that excellence combined with longevity has made for a considerably tougher Hall of Fame path for everyone outside the inner circle. Ron Santo, who ranks ninth in WAR at 70.5, never got more than 43.1 percent of the vote during his time on the writer’s ballot and came up short four times via various incarnations of the Veterans Committee before being elected in 2012, fewer than two years after his death.

Rolen, who ranks just behind Santo with 70.1 WAR, debuted on the ballot in 2018 with 10.2 percent of the vote, the smallest opening share for anyone to eventually earn enshrinement. Edgar Martinez, who ranks 11th in WAR among third basemen but played seven games there after his 32nd birthday and made 68 percent of his appearances at DH, was elected in his final year of eligibility in 2019.

None of the next nine third basemen to debut after World War II and collect at least 50.0 WAR have been inducted. Buddy Bell, Sal Bando, Darrell Evans, Robin Ventura, Ron Cey and Toby Harrah all went one-and-done on the ballot while Graig Nettles fell off after four years. Ken Boyer and Dick Allen stayed on the ballot for 15 years and 14 years, respectively, with Boyer the only player to get as much as 25 percent of the vote.

But the nearly certain presence of the steady and the spectacular on stage at the Clark Sports Center over the next two years — Beltre, who finished with 3,166 hits and the second-most defensive WAR (27.0) behind Robinson, will be on the ballot this fall, when he is sure to at least approach the 96.5 percent of the vote Schmidt received in being elected in 1995 — could help the active third baseman plying their trade in a potential golden era for the position.

“I never saw Brooks Robinson play, but to me, the benchmark, the ideal third baseman, was Scott Rolen — and I felt that way for a really long time,” Chavez said. “The way Scott Rolen played the position from a technical standpoint, from a mechanical standpoint, how you set up, the arm strength, being able to come in on a ball and barehand a ball, go to your left, turn around, rotate and throw, turn double plays — that’s the way that I would teach it. As a matter of fact, when I do talk third base and infield in general, I reference him all the time.”

While Arenado is friendly with Rolen, who will wear a Cardinals hat on his plaque, he has long relied on Beltre as a confidant. Arenado, who turned 32 in April and is signed through 2028, has a .289 average, 320 homers, a 124 OPS+ to go along with five Silver Sluggers and 10 Gold Gloves.

Beltre finished his age-32 season in 2011 with a .276 average, 310 homers and a 110 OPS+ to go along with three Silver Sluggers and three Gold Gloves before he hit .306 with 167 homers and a 128 OPS+ to go along with two Gold Gloves and one Silver Slugger in his final seven seasons with the Rangers.

“I always try to see what he did at (his) age in those years and I try to see if I am keeping up with him,” Arenado said. “And to be quite frank with you, it seems like he kind of just found another gear as he got older.”

Machado, who turned 31 on July 6, has 1,679 hits and 301 homers while winning a Silver Slugger and two Gold Gloves. He signed a contract extension through 2033 earlier this year.

“He’s got more career, he’s got a longer deal,” Arenado said. “There’s no reason why he shouldn’t get close to 3,000 hits at some point.”

In addition, 37-year-old Evan Longoria, who has collected 58.9 WAR while winning three Gold Gloves and a Silver Slugger, has time to author a finishing kick with the Diamondbacks while 30-year-old Jose Ramirez, with 43.7 WAR as well as four Silver Sluggers and four top-5 MVP finishes, is in the prime of his career with the Guardians.

With Rolen and Beltre leading the way, there may be a time in the 2030s when there’s a little more room in the Hall of Fame for third basemen, even if Schmidt may remain in rarefied air all by himself.

“One hundred and six WAR by Mike Schmidt,” Arenado said. “It’s just insane to think about. It’s unbelievable.”