The two players squared off and Crabb got in two solid punches before the teammates were separated by forward Nikolai Kulemin and members of the coaching staff.
Crabb and Gunnarsson continued to glare at each other after the melee, but were taking the altercation in stride after practice.
"We were just battling, it's nothing much," Crabb said. "I thought he butt-ended me, he claims he didn't. That's fine, we were working hard out there, trying to get better. A quick little tussle and that was it."
Gunnarsson had trouble trying to pinpoint what exactly set the two teammates off.
"I don't know what happened," he said with a laugh. "A battle drill, you know, we both kind of snapped. Stuff happens."
"Me and Crabby always got battles going on in practice and sometimes we snap," he added. "But when practice is over, it's over."
Toronto is currently in ninth place in the Eastern Conference, two points behind eighth-place Washington.