The stop-and-start nature of Colton Cowser’s season has prevented him from building on a rookie season that ranked among the best in the American League.

He finished last year as a runner-up in AL Rookie of the Year voting and seemed poised to further that breakout for the Orioles. Yet a broken thumb in the fourth game of the season derailed that. Even after a return to the field in June, the Baltimore outfielder struggled to produce regularly at the plate.

There may still be more questions than answers around Cowser, especially when considering his regression against breaking balls from 2024 to 2025. But on Monday, in the Orioles’ 4-3 loss to the Boston Red Sox, there was a glimmer of that Rookie of the Year candidate.

“Just talking to Colton every day, he’s working his butt off. He hasn’t stopped. He’s stayed optimistic. He’s fun. The whole thing,” interim manager Tony Mansolino said. “A couple of 0-0 breaking balls lately, he’s hit over the fence. I don’t think we’ve ever seen that out of him, so you can see an adjustment’s been made. He’s getting better. Proud of the kid. He’s hung in there through a lot of injuries and time off the field this year, and he’s struggled and he’s been disappointed in himself. It feels like he’s coming out on the other end at the moment.”

Cowser is only 25, so the .692 on-base-plus-slugging percentage with which he entered the series opener at Camden Yards can still be chalked up to the developmental cat-and-mouse game that is adjusting to major league pitching. This second full season, Cowser has seen more breaking balls. And against them, he entered Monday hitting .125 with two home runs — one of which came last week, when he lifted a slider for a homer against the Astros.

And then in the second inning, Cowser caught all of a get-me-over first-pitch curveball from right-hander Richard Fitts. He throttled it for his third home run in four games.

“I think I kind of went through a period where I felt like my timing was off,” Cowser said. “Felt like for me to hit the other stuff, I had to be super on time for the fastball, and I think getting in the cage and continuing to work, it’s one of those things where I realized I have more time than I know. So, just trying to be a little bit more relaxed and making sure when I’m loading, I’m downhill, and when I do that, I can adjust to a lot of things.”

He added a two-run single off Fitts’ changeup in the third inning, and Cowser’s third hit of the game came against left-hander Steven Matz’s sinker.

The home run against the curveball was most promising, however, considering Cowser entered Monday’s game with a 48.6% whiff rate on breaking balls he has swung at this year. He had managed just seven hits against 294 breaking balls in that timeframe.

“He’s probably seeing the most spin in all baseball right now,” Mansolino said.

That’s a considerable difference from what Cowser managed as a rookie. When facing breaking balls in 2024, Cowser produced a .260 average, and against curveballs in particular, he managed a plus-5 run value, per Statcast, tied for second best behind four-seam fastballs.

The recent production from Cowser shows something more familiar. Since returning from a concussion on Aug. 17, Cowser is 10-for-34 with eight runs batted in. He drove in all three of Baltimore’s runs Monday, and he almost saved the Orioles from a Jarren Duran long ball in the fifth.

Instead, Cowser’s leap at the center field fence came up just short, and Duran’s three-run homer against right-hander Tomoyuki Sugano prodded Boston ahead. For Sugano, this marked the first time since July 2 he had allowed multiple homers in a game, as outfielder Roman Anthony led off the game with a solo shot.

“They had an approach for pitches down, especially for the left-handed hitters, particularly the splitter,” Sugano said through team interpreter Yuto Sakurai. “I think they were kind of like focusing on that pitch.”

Sugano completed six innings with four runs against him, and left-hander Grant Wolfram impressed out of the bullpen again behind him. Wolfram pitched two scoreless innings Monday to extend a nearly spotless stretch in which he has allowed one run in 12 innings with 15 strikeouts.

After Gunnar Henderson’s 30th double of the season led off the eighth inning, he was stranded on second because of strikeouts from Ryan Mountcastle, Coby Mayo and Cowser. It was a slider — one of those pesky breaking balls — diving down and in from right-hander Garrett Whitlock that got Cowser to swing through and blemish what had been a perfect night at the plate.

But this did look better from Cowser overall, even if it came in a loss. During a grueling season that has included two injured list stints, there’s an opportunity ahead of him to at least finish the season on a high note.

“There’s a little bit of maturity that comes with it [adversity],” Cowser said, “and I think finishing out this last month strong is going to be huge.”