(Toni L. Sandys/The Washington Post)

Demetrius Hartsfield heard the pop first. A legal cut block felled the Maryland senior linebacker against Georgia Tech on Nov. 3, 2012. Less than three minutes remained in the first half as Hartsfield sprawled on the Byrd Stadium turf. As the pain seared throughout his injured knee, he knew something had popped. He hobbled off the field and tried to run on the sideline, the futile, last-ditch efforts of an injured soul.

“I knew I couldn’t go back in,” Hartsfield said Monday in a telephone interview. “I also knew I probably hurt my team even more. It was tough. Then I started thinking about if I could come back, if that would be my last game. I had a lot of stuff going through my head.”

Clarity came soon for the former captain. He spoke with trainers and relatives, emerging determined to rehab that nasty torn ACL and make a run at the next level. He found an unexpected comrade for the journey in Maryland point guard Brene Moseley, who tore her ACL during a scrimmage on Oct. 21. The sophomore penned an open letter to fans on the Maryland athletics Web site, called “Courage.” Hartsfield found solace in Moseley’s positivity.

Hartsfield can see redemption on the horizon. He sat out the season’s final three games, watching as the Terps labored through losses against Florida State, Clemson and North Carolina, three offenses Hartsfield would have loved to challenge himself against. He estimates he’s around 70 percent, and began running last week. Only straight-line workouts for now. No cutting yet.

The ever-increasing weight stacks on squat machines have convinced Hartsfield that he’s getting stronger each day. He works out with a local trainer named Tobe Stephens and his company ETC, the same company that trains Torrey Smith and Navorro Bowman in the offseason. Right now, former Maryland teammates Darin Drakeford and Devonte Campbell work out with Hartsfield, preparing for their pro day on March 13. Whether Hartsfield attends is uncertain.

“That’s a question I don’t know the answer to right now,” he said. “The next two, three weeks, I’ll know for sure. But it’s not out of the window. I definitely won’t be able to do everything, but I’m still debating with my trainers what I can do.”

His days typically begin around 8:30 a.m. with workouts at ETC, followed by a trip to Gossett Team House for treatment and knee-specific work to strengthen the ligaments and halt swelling. He wants to be 100 percent before summer.

“It’s very tough. I knew I was going to have a lot of limitations,” Harstfield said. “I was just upset because I was honored getting all-ACC also, even though I was hurt. I still felt like if I hadn’t gotten hurt, I could have gotten first team instead of second. I was talking to a lot of teams from all-star games before I got hurt, I more than likely would have gotten a combine invite.

“If I hadn’t gotten hurt, I could be doing all that stuff that I see my friends from other schools doing. It was definitely tough. But I know my path isn’t the same as theirs. I just have to trust that everything will work out right in the end. That’s definitely been helping me a lot. All the people around me have been keeping my spirits high and making sure I’m ok, making sure I take this head on, because it’s not an easy process.”

Hartsfield says multiple NFL teams have contacted his agent, inquiring about the linebacker’s progress. Hartsfield will “definitely” attempt to play linebacker at the next level. With Maryland, he played on the outside and the inside in a 4-3, the inside in a 3-4, so versatility shouldn’t be a problem. Last season, he was the Terps’ leading tackler, despite playing just nine games.

He checks up with Moseley regularly now. Based on Hartsfield’s words, she serves as something of a spirit guide, offering advice for emotionally handling an ACL tear.

Hartsfield seems confident about his professional prospects, even at 70 percent. Drakeford, Campbell and others have kept him plenty motivated for a comeback.

“You got to stay confident and optimistic about it,” Hartsfield said. “That’s the one thing I didn’t want to do — sit around and be like, ‘Okay, my chances are over.’ I believe that’s not the case.”