WEST PALM BEACH, Fla. -- Reliever Brian Ellington threw eight pitches -- all balls -- during his Grapefruit League debut on Sunday against the Braves and was promptly relieved. The right-hander experienced soreness in his throwing shoulder and was diagnosed on Monday with right biceps tendinitis. No MRI was done.
"He's a little sore. He was feeling something," manager Don Mattingly said before the diagnosis. "So we'll make sure he's good. Obviously, he had a little bout of wildness. So we'll see, make sure that's not something physical, and then go from there."
Ellington, whose fastball velocity routinely reaches the upper 90s and even triple digits, was down a little bit. Mattingly said it was the first sign of possible physical problems.
"I watched him throw on the back field a few days ago," Mattingly said. "I thought he threw the ball good. He's been doing extra work, looked good, was progressing. We thought he was starting to turn the corner."
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The 27-year-old, who is 7-4 with a 4.65 ERA, 98 strikeouts and 64 walks over 102 2/3 innings spanning parts of three big league seasons, is a flamethrowing option out of the bullpen.
Peters cites improvement
Left-hander Dillon Peters is hoping to earn a spot at the back end of the Marlins' rotation, but for the second consecutive spring outing, the 25-year-old struggled to find the plate.
Peters went just 1 1/3 innings in Monday's 5-3 Grapefruit League loss to the Astros at FITTEAM Ballpark of the Palm Beaches, giving up a run on one hit and walking three batters -- all in the first -- while striking out as many. He threw 35 pitches, only 13 for strikes.
Miami's No. 15 prospect, according to MLB Pipeline, walked four in just 1/3 inning in his previous outing, coming out of the bullpen to face the Nationals on Wednesday. In his spring debut, he pitched two scoreless frames with no walks against the Cardinals on Feb. 23.
Still, Peters remained positive about the outing because he wasn't missing the plate by much.
"It was more of a nibble instead of a bad miss, so I'm trying to get a grip on that and I'm moving in the right direction," Peters said. "I think it's just a rush of mechanics, a combination of a few things. I thought I threw some good breaking balls that I hadn't felt in like a week. So a combination of a few things made me take away some positives from today."
Peters said he felt cleaner with his delivery and more under control from his last appearance with his tempo, rhythm and timing. He said he's building off that moving toward his next outing.
"It might not show, but I think it got better," Peters said. "I feel good [despite] a shaky first, but big difference in the feeling of the delivery from last start to this start."

Position battle
Brian Anderson has the glove to be a regular at third base and is now showing glimpses of the pop in his bat. With veteran Martin Prado rehabbing from right knee surgery, Anderson is getting extra looks until Prado's return later this spring.
Anderson, Miami's No. 9 prospect, hit a long home run on Friday in Lakeland against the Tigers.
"We think he can be a premier defender at third," Mattingly said. "We think there's a lot of hits in there from the standpoint that he uses the whole field. His power is going to keep coming over time."
The 24-year-old played in 25 games as a September callup, hitting .262 with seven doubles, one triple and eight RBIs in 84 at-bats.

Up next: The Marlins host the Cardinals at 1:05 p.m. ET on Tuesday (listen live on Gameday Audio). Brett Graves, taken in the Rule 5 Draft from the A's, gets his first spring start for the Marlins after appearing in two games out of the bullpen (1-0, 1.80 ERA).