Apparently it takes a lot to make Reeves Nelson come out of the game.

Early in Saturday’s head-to-head matchup of two first place Pac-10 teams, UCLA’s freshman forward literally butted heads with an opponent. On his first possession of the game, Nelson knocked noggins with Cal’s junior center Markhuri Sanders-Frison, causing Nelson to suffer a mild concussion.

“I just knew something was off,” Nelson said. “I just wasn’t right at all in the head. My balance was off.”

But the Bruins’ 6-foot-8-inch, 228-pound low-post enforcer was not about to just stumble out the Pauley Pavilion tunnel.

“At halftime, he went through all the different tests you go through for a concussion,” coach Ben Howland said. “I asked him point blank if he was okay and he said “˜yeah.’”

Although Nelson returned for much of the second half, his 20 minutes of game time was his lowest total since playing against New Mexico State back in December. He also only had six points in the game, the fewest he’s scored since that same week in December, when he made just one field goal in the John Wooden Classic.

That’s not to say he didn’t get an “A” for effort, though.

“I’ve always been like, if I can walk, then I’m going to play,” Nelson said. “I think next time I’ll take it easier. Hopefully, it doesn’t happen again.”

This isn’t the first injury Nelson has suffered this year as a result of his rough-and-tumble style of play. Two months ago, a stray finger found his eye on a drive to the hoop against top-ranked Kansas, an incident that resulted in a corneal abrasion, a brief trip to the hospital, and a new pair of yellow sport goggles. Oh, and he made the shot.

Once back in the game against Cal, Nelson shrugged off the possible cranial damage by joking around with Sanders-Frison.

“We were talking about how we both felt really dizzy on the court, but we were both just going to stay in and play,” Nelson said.

After meeting with a doctor on Tuesday, Nelson was cleared to participate in non-contact practice. He will most likely be cleared for contact by Thursday’s practice, but Nelson doesn’t see the injury as a continuing problem. In fact, he had no doubts about participating in the team’s rematch against rival USC at the Galen Center this Sunday.

“Oh, I’m definitely going to play no matter what,” he said.

The Trojans boast two of the conference’s best rebounders in 6-foot-10-inch Nikola Vucevic and 6-foot-9-inch Alex Stepheson. But Nelson, as always, is pretty confident when it comes to standing his ground.

“Those are two big, strong players, so it’s kind of tough matching up against them,” he said. “But we’ll be fine.”