The Mets' Amed Rosario heads up the first base line...

The Mets' Amed Rosario heads up the first base line after hitting a two-run home run off Rockies starting pitcher Tim Melville during the sixth inning on Tuesday in Denver. Credit: AP/David Zalubowski

For Amed Rosario, averageness has never felt so successful.

Through the ups and downs of his second full major-league season, Rosario heads into the Mets’ final 10 games, starting Friday in Cincinnati, with a .287 average, .324 OBP and .427 slugging percentage. That is both both merely league average and major progress from last season, evidence that Rosario — still just 23 — continues to develop and is heading in the right direction.

“He has improved in every facet of his game since first saw him two years ago,” manager Mickey Callaway said. “Just a more disciplined hitter than he was in the past, and he continues to grow every day.”

How do we know that Rosario is average? His slash line results is an OPS+ of 101. OPS+ is on-base percentage plus slugging percentage, adjusted for ballpark factors and set so that 100 is average — a sort of bottom-line measure of offense that compares a hitter to his peers in a given year. In a similar modern metric, weighted runs created plus, Rosario is at 98.

Those are both steps up from Rosario’s 88 OPS+ and 85 wRC+ in 2018, which were steps up from his 76 OPS+ and 75 wRC+ during his rookie partial year in 2017. More jumps of that degree would make Rosario the offensive-threat franchise shortstop the Mets thought he would be.

Here are three areas in which Rosario has improved this year:

- Hitting with two strikes. Callaway highlighted this trend this week as the Mets won a series against the Rockies.

Rosario last year with two strikes: 51 hits and a .180/.215/.239 slash line.

Rosario this year with two strikes: 67 hits and a .229/.263/.307 slash line.

“It’s something I’ve been working on since I was in the minor leagues,” Rosario said through an interpreter. “It’s pretty much trying to clear my mind of having two strikes, because once you start thinking that you have two strikes, you think, ‘Oh man, I can strike out.’ So it’s something that I take out of my mind at that point. That’s how I’ve been able to succeed.”

Callaway said: “That is hard, especially to do it at the major league level like he’s done. He didn’t have a ton of reps (in the minors). … Tough thing to do, and you have to give (Rosario) credit for making such good strides.”

- Hitting the ball harder and farther. Power is often one of the last skills a hitter develops, and in Rosario — sneaky strong but still lanky — the progress is evident here, too.

Last year, Rosario’s batted balls came off his bat at an average of 87.3 mph, which is about average across the majors. This year, his hit speed is up to an above-average 89.4 mph.

Among those who rank similarly: the Reds’ Eugenio Suarez, who is challenging Pete Alonso for the homer title; the Blue Jays’ Vladimir Guerrero Jr., who debuted this year to as much hype as any prospect in recent memory; and the Astros’ Alex Bregman, who is an AL MVP candidate.

Combine Rosario’s more frequent hard contact with a bit more air time, and it means higher-quality batted balls that have more often gone for hits and extra-base hits.

- Controlling the strike zone. A proud Rosario doesn’t hesitate in answering in which area he has made the most progress in 2019: “My recognition of the strike zone.”

Last year, Rosario swung at 41.2 percent of pitches outside the zone, according to FanGraphs. This year, he has that down to 37.5 percent.

Rosario, relatedly, has drawn two more walks in seven fewer games compared to last year.

“That is something that, in the future, can be really beneficial for me,” he said. “Something also I’ve taken pride in is my ability to walk.”

Put it all together and you get an average hitter who has made significant strides with room, it seems, for much more.

“I think I’ve actually had a pretty good year,” Rosario said. “Obviously there are going to be ups and there are going to be downs, but when you have those ups you have to take advantage of those moments, because it is a hard game.”