Opponents batted just .199 against Brandon Walter last season at the Class A level. In his final nine starts for High A Greenville, Walter struck out 36.3 percent of the batters he faced. Photo courtesy of the Greenville Drive

Chad Epperson, new manager of the Portland Sea Dogs, spent the previous dozen seasons as catching coordinator for the Boston Red Sox. He traveled throughout the organization’s farm system and worked with catchers at every level.

Not every moment was focused on their development as receivers of the baseball.

Epperson listened closely when the catchers spoke of the challenge presented by certain pitchers, even during bullpen sessions. Occasionally, he would hear, “Oh man, he’s a tough catch.”

Brandon Walter

That’s when he first took notice of Brandon Walter, a 25-year-old left-hander set to make his Double-A debut Sunday at Hadlock Field.

“He’s going to challenge a catcher to be on his ‘A’ game,” Epperson said, “because his stuff is electric.”

Few minor leaguers make their debut on top-prospect lists when they’re as old as Walter, who entered the professional ranks without much ballyhoo. In the 2019 draft, he was passed over for two days before the Red Sox made him their 26th-round selection, 797th overall.

Delaware is not known as a hotbed of baseball talent, so growing up there and pitching for the University of Delaware made it tougher for Walter to be noticed. An arm injury early in his sophomore season led to Tommy John surgery, which wiped out the rest of 2017 and all of 2018.

He wound up starting 14 games for Delaware as a redshirt junior in 2019. The Boston Red Sox took a chance and signed him for a reported $35,000. He expected to join their more advanced short-season club in Lowell, Massachusetts, but instead was sent to Fort Myers, Florida, to pitch in the rookie-level Gulf Coast League.

“I was a 26th-rounder,” he said this week after working out at Hadlock Field for the first time, “so I knew I wasn’t going to get treated like royalty.”

After making 37 starts in college, Walter pitched exclusively in relief to finish out his 2019 season with Fort Myers. He put up solid numbers – 39 strikeouts and eight walks in 33 1/3 innings while holding batters to a .208 average – but his year “was not one that projects to having a lot of success,” he said. “I knew I had to make a lot of changes.”

Then came 2020, when the pandemic wiped out minor league baseball. Where others lamented a missed opportunity for further seasoning, Walter embraced the time to build up his body and improve his mechanics. He added 10 pounds of muscle to his 6-foot-2 frame and 5 miles per hour to a two-seam fastball that had been in the high 80s.

“That’s a significant jump for me,” he said. “I’ve always been the guy who can throw strikes, so I’m glad with the velocity jump and the uptick in stuff that didn’t change.”

Walter also throws a slider and change-up, both in the low 80s, from an arm slot somewhere between three-quarters and fully sidearm. Call it five-eighths. That motion gives his pitches considerable lateral movement, which is why catchers can’t get complacent.

He started 2021 in the bullpen at Low-A Salem, moved into the rotation in late June and after two starts earned a promotion to High-A Greenville. He made 12 more starts with Greenville and over his final nine struck out 65 of the 179 batters he faced, a rate of 36.3 percent. Over the entire season, opponents batted .199.

He enters this spring ranked among the top 10 Red Sox minor leaguers by FanGraphs, MLB.com and SoxProspects.com. Because of the lockout, he also spent time this spring with the Red Sox big-league staff, including Boston pitching coach Dave Bush and Manager Alex Cora. It was Cora who watched a bullpen session and told Walter he would hold his glove differently before throwing a change-up.

Reed Gragnani, the former Sea Dogs infielder and current roving hitting instructor, was the Red Sox scout who followed Walter in college and signed him. Gragnani, speaking from home in Virginia, said both times he saw Walter pitch at Delaware, only one other scout was in attendance.

“The constants are still his strike-throwing ability and his change-up has always been good,” Gragnani said. “The velocity has ticked up and he’s committed to a slider that he didn’t have as an amateur. It has become an above-average pitch for him.”

They still talk, most recently at spring training in Fort Myers.

“I saw him quite a bit this spring,” Gragnani said, “because he got a lot of my hitters out.”