Seth “Mayhem Mitchell” has a 22-0-1 record with 16 knockouts. He says he sees himself fighting for the heavyweight title by the end of 2013. (Mark Gail/THE WASHINGTON POST)

Inside Dream Team gym, a former auto repair garage in Clinton, Seth “Mayhem” Mitchelldelivers body-shaking blows.

Punch after punch, his trainer, Andre Hunter, re-grips a padded medicine ball just to hold on. Mitchell unleashes another right hook. Boom.

The medicine ball plops to the mat.

Mitchell, 29, paces the boxing ring in a gym decorated with posters, mirrors and punching bags, as he waits for Hunter to recover and continue with the simulated seven-round bout. Time is ticking away. Mitchell is less than two months from the biggest fight of his career, his HBO debut against a so far undetermined competitor on Aug. 27.

Known not only for his power, but for his quick hands and feet, Mitchell is undefeated as a professional and has ascended into the top 100 heavyweight fighters in the United States, with a 22-0-1 record in three years.

“Pain,” Hunter said in describing Mitchell’s punches after Wednesday’s workout. “If we haven’t been doing it for a while, I’m sore and I’m trying to figure out where this injury comes from and where that injury comes from. And sometimes I’m bruised real bad.”

Mitchell, who is 6 feet 2 and weighs 245 pounds, threw his first punch at a middle school Halloween dance. The kid was a bully, Mitchell recalls. He stood up to him and won his first and only fight in school.

He played football at Michigan State before a knee injury cut his career short and, in an almost spur-of-the moment decision, he took up boxing.

“The ring is my home now,” Mitchell said. “This is the new football field.”

Mitchell’s televised debut on Showtime May 13 against Nicaraguan Evans “The Sandman” Quinn ended in the first round with his seventh consecutive knockout and 16th overall. “I like being in this position, when the stakes are high,” he said. “As long as I continue to progress, as I’ve been doing, before the end of 2013 I see myself fighting for a title.”

Dan Rafael, an boxing writer who has followed Mitchell since his debut, has called him the best American heavyweight prospect. “He has had a very steep learning curve,” Rafael said. “He has improved in a very short period of time. He’s still very untested. But there’s still a lot to be proven between now and when he fights for a title, if he gets to that point. [Aug. 27th] is a very, very important fight for him.”

Gwynn Park honors

Mitchell’s passion for competition flourished at Gwynn Park High School where, as a linebacker, he became the first football player in school history to have his jersey retired. He finished his senior year with 146 tackles, 9 sacks and 6 interceptions to lead the Yellow Jackets to a berth in the 2A state championship. He was the 2000 Associated Press Maryland Defensive Player of the Year and also earned all-American and Washington Post All-Met honors.

Mitchell rode his success to a full scholarship at Michigan State, where a sprained right MCL sidelined him for his freshmen season. Knee inflammation forced him to sit out the first five games of the next season, although he returned to start five games.

Mitchell tallied 103 tackles as a redshirt sophomore, despite dealing with sharp pain in his knee. He spent the next year trying to recover from knee surgery, but soon the pain was too much.

“One day I said, ‘enough is enough’ and I walked away from the sport,” Mitchell said. “When I made my decision, I was ready to make it two years earlier. . . I felt I did everything in my power to continue my career and it just wasn’t working.”

Team Mitchell

In 2006, Mitchell called home to Brandywine to tell his mother and his high school coach, Maurice Banks, that he was coming home to take up a new profession, one that had nothing to do with his criminal justice degree.

A few days earlier, he had watched former Notre Dame safety and current Baltimore Raven Tom Zbikowski make his professional boxing debut at Madison Square Garden. The move meant leaving his future wife, Danielle, who was pregnant with their daughter, Aurielle, at the time and starting a boxing career with no experience.

“I never really heard him talk about boxing before,” Danielle said. “I never really noticed that he was a fan of boxing. He just said, I think it’s something that I could be good at. . . . For the most part, it was like ‘Okay, if that’s what you want to do, how can we work this out?’ ”

“Team Mitchell” didn’t take long to form, starting with Manager Sharif Salim, who put Mitchell in touch with Hunter. After knocking out nine of 10 boxers he faced as an amateur, Mitchell debuted as a pro in 2008. After winning his first fight, he signed with Golden Boy Promotions, the organization founded by former champion Oscar De La Hoya.

“When I go back and watch the fight, I look terrible,” Mitchell said.

On Wednesday morning, Mitchell donned his Michigan State green mesh shorts, which match the boxing shoes he painted green. He arrived to work out carrying a white plastic trash bag half-full of boxing gear and his water bottle, a gallon-sized Tropicana orange juice jug.

Mitchell completed a regular workout, which included seven rounds inside the ring pounding heavy mitts worn by Hunter. He finished the day with 10 minutes of jumping rope, a simulated speed bag workout, abdominal exercises and a four-mile run. When there are six weeks left until his fight, Mitchell will go 15 or 16 rounds in the ring before he gradually gears down toward the last couple weeks in August.

“I believed in myself from Day One when I said I was going to box,” Mitchell said. “I knew I could do great things in this sport. . . . I want to be financially secure and be able to let this be a platform for other things and take care of my family.”