ST. PETERSBURG — The Tampa Bay Rays’ outfield defense has vaulted from one of the worst units in baseball to one of the best, a turnaround driven by first-year outfield coach Corey Dickerson and a revamped approach to pre-pitch preparation and reaction-time training at Tropicana Field.

Rays outfielders entered the series opener against the Angels with 10 Outs Above Average, according to Statcast — third-most in the Majors behind the Red Sox and Cubs. They also rank third in Fielding Run Value, behind the same two clubs. Last season, Tampa Bay’s outfielders finished 21st in the Majors in OAA and 26th in FRV.

“It’s pretty cool,” manager Kevin Cash said, describing how shortstop Taylor Walls and left fielder Chandler Simpson now move in sync on batted balls. “They’re kind of in line.”

Simpson has made the most dramatic individual leap. After getting essentially average jumps last season, he now ranks eighth among qualified outfielders at 3.1 feet above average, as MLB.com’s Mike Petriello detailed. “Just anticipation, that’s what me and [Dickerson] have been preaching. Just playing offense on defense, being aggressive,” Simpson said. “Reading the ball, reading swings, reading situations.”

Veteran Cedric Mullins told a similar story. Unhappy with his defensive performance last year, Mullins said one conversation with Dickerson clarified what needed to change. “I know that’s not me as a defensive player. I wanted to definitely improve upon that as quickly as I could,” Mullins said. “He came in with a true plan for us, and it’s been working really well.” Mullins has gone from posting below-average reaction times throughout his career to having one of the quickest first steps in baseball this season.

Jonny DeLuca, currently working his way back from a hamstring injury, was also getting below-average jumps last season despite his strong defensive reputation. When healthy this year, he has been among the best in the Majors, pairing athleticism with quicker reactions. Dickerson introduced a pre-pitch hopping technique — common among infielders but new to DeLuca in the outfield — during spring training. “Having some of the data come out and be like, ‘Oh yeah, I’m getting good jumps,’ it’s encouraging,” DeLuca said. “He’s played a major role in that. He’s just been there and done it, and having a guy like that who has done it very well and has had success, it’s easy to listen to a guy like that. He’s been a great listener, too, getting the feedback from us on what helps and the individuality of each and every player.”

Dickerson credited the players’ buy-in, citing “the quality of athletes we have, but also how much they care to prepare.” His methods include drills borrowed from tennis and other reaction-dependent sports — tossing small, bouncy balls to bare-handed outfielders along the right-field line hours before first pitch. “But it’s the mental side that makes a drastic change, that makes the biggest jumps,” Dickerson said. “The consistency of the drill work we’ve been doing has really paid off, and the guys are willing.”

Simpson said the coaching has been relentless in the best sense. “He knows the mentality that you have to have to make that jump,” Simpson said, “and he’s on us every day about it.” The Rays continue their homestand against the Angels at Tropicana Field through the weekend.