A side-winding reliever who simply gets hitters out -- 31 up, 28 down, two hits and a walk interrupting the procession thus far this spring -- O'Day has thrust himself into contention for a middle relief role expected to surface at the start of the season because of Chris Bootcheck's oblique strain.
It turns out O'Day, a 6-foot-4 right-hander from Florida, has his own secret weapon: brother Kyle, a certified athletic trainer in Gainesville, Fla., who spends much of the year touring the world, working with elite sprinters on the pro track and field circuit.
"I talk to him every day," O'Day said on Wednesday at Tempe Diablo Stadium. "He has a tremendous amount of knowledge about the body that's really been helpful to me. He gives me advice on supplements, lifting, nutrition.
"A lot of his work applies kinesiology. He's given me a lot of insights I've been able to use."
Kyle isn't the only educated O'Day. Darren is smart enough not only to spell kinesiology, but to know what it means.
A pre-med student at the University of Florida in Gainsville, he initially wanted to be a veterinarian, focusing on equine treatments. Shifting to standard medicine, he was accepted into medical school at Florida.
But, at the behest of Tom Kotchman -- Angels superscout and proud father of their first baseman, Casey -- O'Day's passion for baseball prevailed.
Kotchman was working his turf in Florida when he saw something he liked in O'Day, the University of Florida's closer. As a fifth-year senior whose team didn't reach postseason play, Darren was able to choose the club he wanted to sign with. Tom Kotchman, persuasive and caring, made that an easy decision.
"I owe him a lot," O'Day said, having spent his first 14 professional games as a pitcher under Kotchman's supervision with his Rookie ball team in Orem, Utah. "He's given a lot of guys like me a chance. [Scot] Shields worked out pretty well."
Signing at 23 and moving quickly up the ladder, O'Day finished 2006 at Class A Cedar Rapids, and divided his 2007 season between high Class A Rancho Cucamonga and Double-A Arkansas.
He's 10-6 with a 2.57 ERA in 84 Minor League games, finishing 67 of them. His maturity has been evident in the confident manner in which he has handled hitters this spring.
And he owes it all, indirectly, to a summer beer league back home in Jacksonville, Fla.
After attending Bishop Kenny High School in Jacksonville, O'Day passed up Division II offers to go to the University of Florida and attempt to walk on the baseball team. After he was unable to claim a scholarship his freshman year, he tried something new.
Abandoning his standard overhand throwing motion, O'Day experimented with a side-arm delivery in a beer league. It came naturally, throwing those beer-league sluggers off balance, and soon it became his ticket to a scholarship and big things at Florida as the team's closer.
"I never was one to overpower guys with my fastball," O'Day said. "With this delivery, all my fastballs are sinkers. If it's a good fastball day, I'll stick with it. If not, I can go with two sliders -- one I throw early in the count with a little break for strikes, the other I throw late in counts that has a more sweeping break."
Angels manager Mike Scioscia has seen O'Day mesmerize Major League hitters this spring, striking out 10 in his 9 1/3 shutout innings. He's been the winning pitcher in two of his five appearances, and he also has claimed a save.
"He's on our depth chart," Scioscia said. "He's going to have some opportunities to show us what he can do.
"I'm not going to say he wasn't on our radar coming into spring, but he's certainly opened some eyes a little further. He's been lights-out."
The Minor League reports were favorable, but there was nothing to suggest O'Day would be virtually unhittable.
"With Darren," Scioscia said, "his 'MO' in the Minor Leagues is he throws strikes and hits spots."
O'Day essentially has been a back-end, one-inning pitcher: 91 innings in 84 Minor League appearances, with 27 walks and 77 strikeouts.
Scioscia thinks O'Day can stretch it out as a middle reliever, if necessary.
"I think he'll have the length we're looking for," the manager said. "If he has the durability to repeat it in consecutive games, that'll make him a candidate."
O'Day isn't about to get beyond himself, thinking only in terms of the moment.
"I'm enjoying this," he said, beaming. "This has been a great experience."
Brother Kyle is hearing all about Darren's great adventure on a daily basis.
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.