SCOTTSDALE, Ariz. — On social media and inside the stadium, on talk radio and at the pub, no major-league player is more polarizing than the Giant who laces those size-15 cleats and trots to first base every night.

Brandon Belt is the best power hitter on the team, Brandon Belt strikes out too much. He is a great defender. He will never be a Gold Glover. His sense of humor is endearing. His body language is terrible.

The five-year, $72.8 million contract extension that Belt signed in 2016 is a fair deal and other teams would love to have him. The Giants will live to regret that contract. Trade him!

Nowhere is the divide greater than inside the equally polarizing world of statistics.

Many old-schoolers scoff at a 6-foot-5 first baseman with a .268 career batting average who turns 30 in April, has not surpassed 18 homers nor 82 RBIs in any season, and strikes out a ton.

But Belt is a sabermetric darling who might be worth more than the $16 million he will earn in 2018 as the big-money portion of his contract extension takes effect — or so say those who swear by Wins Above Replacement.

“He does a lot of things we like to see under the hood,” said Eno Sarris, a longtime Fangraphs reporter based in the Bay Area who was just named national analytics writer for the Athletic.“He’s got a great walk rate. He’s been a really good defender at first base. He has great non-homer power. He’s really good at spraying the ball around the field. I don’t know if people would know this, but he’s tied for 22nd in baseball in doubles the last three years, and he’s had way fewer plate appearances than (almost) everybody on the list in front of him.”

Indeed, the 21 major-leaguers ahead of Belt have averaged 1,946 plate appearances since 2015. Injuries (including concussions) have limited Belt to 1,662.

Another popular metric is wRC+, which tries to measure how many runs a player creates with all the singles, doubles, homers, etc. that he produces, adjusted to eliminate variances in the two leagues and 30 ballparks.

Belt’s career wRC+ is 28 percent above the major-league average. By comparison, Eric Hosmer, who is 18 months younger and just signed an eight-year, $144 million contract with the Padres, has been only 11 percent above average.

Belt’s wRC+ in 2016 was 37 percent above average, which pushed him to the precipice of “great,” according to a chart in the Fangraphs glossary.

Belt is well aware of the divide. When told that The Chronicle wanted to write about it, he smiled and said, “You mean why I look so good on paper and look (so bad) in person?”

“I can’t help what people think,” Belt said. “All I can do is play my game and let the numbers speak for themselves, whether that’s your traditional numbers or whether that’s metrics.

“I would say that I pay attention to some metrics because the traditional numbers don’t always tell the full story.”

Belt’s story in 2018 will depend largely on whether he can avoid another concussion. His fourth cost him the final two months of 2017.

He has shown no ill effects during spring training, physically or psychologically, after acknowledging that he lapsed into a depression and behavioral change following his concussion that carried well into the offseason.

One need not parse many numbers to understand Belt’s subpar 2017 season before the Aug. 4 concussion.

He got pull-happy and hit a lot more groundballs into the shift, which contributed mightily to a 34-point drop in his batting average from 2016. He needs to return to what made him a good hitter and use all fields.

Belt was tracking toward a career-high 28 homers when his season ended, but also a career-high 162 strikeouts. Whiffs are not a sin in modern baseball. Yankees rookie Aaron Judge struck out 208 times last year, but he also hit 52 home runs.

Maybe fans would let up on Belt’s strikeouts if he hit for that kind of power, but that will not happen when he plays half his games at AT&T Park. And, though Belt insists he is not pouting when he returns to the dugout after a strikeout, fans still read his body language that way.

“We prefer our stars to be alpha males and never really show their struggles,” Sarris said. “In a way, criticizing his shoulders is criticizing him more as an actor than a baseball player. You can look across the bay. Khris Davis has similar shoulders and a similar kind of gait. People read it very differently for some reason.”

Belt wants to cut down on strikeouts, but not at the expense of what makes him so good at reaching base.

One big knock on Belt is the number of hittable pitches he takes, a product of having one of the best eyes in the game. He walks a lot, understands the importance of reaching base and often lays off pitches an inch or two off the plate that get called strike three.

“You’re right,” he said, “I leave it up to the umpire sometimes, but that’s my approach and I don’t think I’m going to change that, because it gives me the best opportunity to be successful.”

A much bigger paycheck could ratchet the pressure on Belt to be successful in 2018. He is confident he will be worth the money.

“I haven’t thought about it at all because they signed me for what I was doing,” he said. “I’m 100 percent positive I can do that and more. I’m not worried abut it. I’m just going to go out there and play my game, be a good teammate and help this team win, and that’s all there is to it.”

Henry Schulman is a San Francisco Chronicle staff writer. Email: hschulman@sfchronicle.com Twitter: @hankschulman

Belt’s MLB stats