Red Sox reliever Garrett Whitlock has not allowed a run this season in 11 1/3 innings of work. Steven Senne/Associated Press

Garrett Whitlock has not only been the Red Sox’ most surprising pitcher out of the bullpen, but one of the best arms on the pitching staff this season.

So why isn’t he pitching more?

The 24-year-old Whitlock, selected in last December’s Rule 5 draft from the Yankees, has still yet to give up an earned run in 11 1/3 innings over five appearances in his rookie season. He’s struck out 14 and allowed just one walk. He’s become one of Alex Cora’s best weapons, armed with a devastating changeup that’s been a nightmare for his opposing hitters.

Given how successful he’s been, there could and should be a temptation to use him more than he has over the first 23 games. But there are some variables at play. It’s not only his first season in the majors, but this is also his return from Tommy John surgery. Before this spring training, when he emerged almost immediately to Cora as a major league-ready arm, the last time Whitlock pitched in a competitive game was in July 2019, and that was at the Double-A level.

The Red Sox, as impressed as they’ve been with Whitlock, don’t want to put more on his plate than he’s ready for.

“He’s pitched really well,” Red Sox pitching coach Dave Bush said. “He’s certainly performed well enough to have a better role but there’s still a lot of factors here. He missed the whole year because of Tommy John. It’s his first time in the big leagues. We’re trying to be smart about how we use them and make sure we develop him appropriately. Sometimes the tendency or the temptation can be to put too much on guys like that too soon, simply because they start out really well.

“But we’re trying to be cautious and trying to do the right thing for him, so we found a couple of situations lately where he can pitch multiple innings, and he can continue to gain experience. He’s gonna have some bumps in the road sometime soon. He’s gonna have some games that aren’t great for him and that’s part of the learning process. So want to make sure we allow him to develop and learn from those things at the right pace.”

Cora said last week that the Red Sox see Whitlock as a starter in the future, though it’s unclear when. For now, the Red Sox have been using him for multi-inning relief appearances every four or five days, a role he’s excelling in even if it seems like he could be giving more. One thing is certain: Since he’s a Rule 5 pick, he has to remain on the Red Sox’ 26-man roster throughout this season or be offered back to the Yankees.

The way he’s pitched, there’s almost a 100 percent chance he’ll stay on the active roster for the whole season. Now it’s just about finding the most suitable role for him.

“I don’t know what his role is going to be the rest of the year,” Bush said. “It might become bigger, it might be more length, it might be more frequent shorter outings, but he’s done a lot of things really well up to this point so we’re going to continue letting him pitch and see where we go with him.”

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