His love of wrestling evolved into a love of competitive mixed martial arts — a sport his father did not view as appropriate for a Muslim. “Youssuf is a pretty strict, straight-line Muslim guy,” Mr. Jones said.

A video uploaded in July 2009 to GoFightLive, a YouTube account that collects video of mixed martial arts fights, showed Mr. Abdulazeez in camouflage shorts, participating in a cage fight with a man identified as Timmy Hall. Mr. Abdulazeez dominated the fight, pinning his opponent to the mat early and pummeling him.

Chet Blalock, former owner of a mixed martial arts gym in Chattanooga where Mr. Abdulazeez trained, said Mr. Abdulazeez, would allow himself to be choked while fighting until he lost consciousness. Several times, he recalled, the young man would be out cold, revive himself, then take a brief breather before continuing to train.

“It’s a bit on the extreme side, even for mixed martial arts,” Mr. Blalock said. He now thinks that Mr. Abdulazeez may have been testing his threshold for pain.