Matt Barnes knows his role with Red Sox

Pitching attrition is a constant in baseball, and with every instance of it comes a reminder: Seasons often pivot on how well-suited a team is to withstand the inevitable injuries to its collection of arms. Matt Barnes may have a prominent say in the Red Sox’ answer.

At a time when Eduardo Rodriguez is set to miss at least the first few weeks of the season, Barnes already loomed as a potential early-season multi-innings option out of the bullpen. But with Monday’s more ominous injury to righthander Carson Smith (strained flexor in his right forearm), the Red Sox may have to reconfigure their bullpen blueprint. And if that happens, Barnes appears to be the pitcher best positioned to help fill the void.

This spring is different for the 25-year-old Barnes. He knows he’s preparing for a season as a reliever.

A year ago, the picture was cloudier.

The Sox were undecided about whether his role should be in the rotation or the bullpen. His passage through the season at times resembled an effort to navigate a highway during rush hour, Barnes rendered somewhat uncertain about which gear to employ, how hard to step on the gas pedal, and how long he could keep it down.

“I had so many times last year where you have to figure out how to relieve, then back to the mind-set of being a starter, then back,” said Barnes. “It made it a little tough last year. I was kind of unsure of how to use my stuff.

“Going to the bullpen, I was like, ‘Awesome, one or two innings, I can just kind of let it loose.’ That doesn’t work that well if you’re not going to locate your stuff.

“I almost got excited, thinking I could throw incredibly hard now. But incredibly hard down the middle in the big leagues gets hit. It will either flatten out or run to the middle. It doesn’t have the same carry through the zone, dropping the arm and using the body to make it throw harder, as opposed to staying on top of the ball, working downhill, and angling it.”

The lesson arrived in uncomfortable fashion. A promising start (1.93 ERA and innings of increasing consequence through 12 starts) ran off the rails. For a month starting in early June, he allowed 11 runs in 8⅓ innings, with opponents tattooing him for a .410 average that resulted in a trip back down to Pawtucket, a return to the rotation to try to regain feel for his complete pitch mix, and more uncertainty.

In both his preparation for his roles and his execution in them, for much of the year, Barnes struggled.

“I think last year was challenging for him settling into a routine,” said PawSox pitching coach Bob Kipper. “Starters have routines. Relievers have routines. They’re different.”

Ultimately, Barnes proved capable of absorbing some of the hard-earned lessons that opposing hitters and situations presented at the big league level. After a pair of ill-fated starts (13 runs in 10⅓ innings) in mid-August, he went back to Pawtucket. When he finally returned in September as a reliever for the final three weeks, he became a different animal.

Barnes closed the year with nine appearances in the big leagues in which he had a 0.87 ERA with eight strikeouts and three walks in 10⅓ innings. During that time, he increased his fastball and changeup usage while spending less time throwing his curveball.

Yet instead of reaching back for velocity, Barnes found that he had greater movement and command with a less effortful delivery — with little decrease in his velocity, averaging 94.5 miles per hour down the stretch.

“I toned it back, realizing how everything was going to play — being smarter and continuing to pitch instead of throwing,” said Barnes. “You’re still throwing all your stuff aggressively in the zone, but make sure if you’re going to miss, you’re not missing middle. You’re expanding — going up, going down, and still not trying to do too much.”

He carried that approach into this spring, during which he’s been one of the Sox’ most impressive pitchers. Barnes has thrown 8⅓ scoreless innings while striking out nine and walking just one while permitting a scant five hits, showing power, command, and stuff.

He’s throwing a tighter curveball with a sharper, narrower break, whether for strikes or as a chase pitch below the zone. Kipper also noted Barnes’s progress in incorporating a strike-stealing slider to further vary his looks.

But ultimately, his success will ride on one central element that makes him the best candidate for a power arm to spare the overuse of Craig Kimbrel, Koji Uehara, and Junichi Tazawa should Smith be lost for any period of time.

“Success is going to hinge on his ability to command No. 1, his fastball,” said Kipper. “That’s Matt’s greatest weapon.

“The mix is there to be a very solid reliever. He went through a lot last year, was challenged last year, and at the end of the day, we know he had a really impressive September. That speaks volumes to Matt Barnes and his personality.”

Barnes knows where the Sox will want him to contribute in 2016. In that certainty comes possibility as the Sox mull potential alternatives in Smith’s absence.

As Nick Cafardo writes, the Mariners wondered whether Smith’s unusual delivery might lend itself to injury risks when they traded him to the Sox as the key to the Wade Miley deal.

Alex Speier can be reached at alex.speier@globe.com. Follow him on Twitter@alexspeier.