The shape of Aaron Brown’s future is the octagon.

Three years after completing his University of Hawaii football career, Brown makes his professional mixed martial arts debut Saturday in Mesa, Ariz.

Brown, who was the St. Louis Rams’ seventh-round pick in 2012, said he has retired from football.

"I’m all in," Brown said of his MMA career. "I’m fighting to be the best. I’m fighting to be a world champion one day."

Brown faces Casey Greene in a five-fight event billed as "Dual For Domination 8" in the Arizona Event Center.

Brown is following the path of former roommate and UH teammate Jake Heun, who also is an MMA fighter.

"I kind of talked to him a little bit to see how to get started," Brown recalled. "He let me know. He’s kind of doing his own thing, and I’m doing my own thing."

Brown began working out in Washington state, where he was raised, before moving to Gilbert, Ariz., in January.

Brown trains at Power MMA & Fitness, the home base for UFC competitors Ryan Bader, CB Dolaway, Gray Maynard and Ryan Jimmo.

"I’m holding my own," Brown said of his sparring sessions.

Brown will fight at 205 pounds, 15 pounds lighter than his playing weight as a UH outside linebacker. As a former high school wrestler, Brown noted, "the ground game came natural to me."

His workouts are divided into boxing, Brazilian jiu jitsu, boxing, wrestling and muay thai.

He has traded football’s power-lifting for circuit training involving so-called explosive, high-intensity lifts.

"In football, you’ve got 20 seconds of full go and then you can rest," Brown said. "In MMA, you have five minutes (each round) of straight 100 percent go. You have to pick the timing, and when you can use power and strength, so you don’t gas out."

Brown won his lone amateur fight earlier this year. He said the plan is to eventually drop to the 185-pound division and move up in classification.