PROVO — The way BYU's Harvey Unga is performing in scrimmages, it may be difficult to keep him off the field once the games begin.

Unga, a redshirt freshman running back, starred again Saturday as the Cougars held a 52-play scrimmage at LaVell Edwards Stadium. After rolling up plenty of yardage against the BYU defense, Unga scored on a 26-yard run down the sideline for the only touchdown of the day on the final play of the scrimmage.

"Every day's an opportunity to get better," Unga said. "The coaches told us to stick to what we learned in our meetings. (Running backs) coach (Lance) Reynolds knows what he's talking about. He's been around the game long enough to teach us what to do, and if you do it, you're going to have success."

Still, with less than two weeks to go before BYU opens the 2007 season at home against Arizona, coach Bronco Mendenhall held out several key starters on both sides of the ball as a precautionary measure. Considering the number of players who have been lost for the season during fall camp, no one could blame him.

Linebackers Bryan Kehl and David Nixon and safety Quinn Gooch were among those who played sparingly.

"This day wasn't about ones against ones, it wasn't about the execution of each unit," Mendenhall said. "What it was is a lot of personnel identification, especially for key backup roles and establishing some depth. It was a positive day for what we wanted to get accomplished."

Starting quarterback Max Hall led the first team on four drives, which included three scores — two field goals and Unga's TD.

"As an offense, we moved the ball a lot today. We had a few mistakes and penalties, but other than that, it's pretty good," said wide receiver Michael Reed. "But as we have been saying all year long, being pretty good isn't going to get us another Mountain West Conference championship or BCS bowl bid. We've just got to come out here and be great, especially on this field. We need to make sure we win every game at home."

Running back Fui Vakapuna didn't participate in Saturday's scrimmage. Vakapuna underwent foot surgery during the off-season and is trying to lose some weight. Mendenhall is taking a cautious approach.

"We still have two weeks to go, and he's made some significant progress," Mendenhall said. "Instead of taking a step back and risking further injury, I'd rather take it step by step. He's still not completely ready."

In Vakapuna's absence, Unga filled in admirably. Fellow running back Manase Tonga will miss the Arizona game due to a suspension, which means Unga's role could be big from the beginning.

"Of course, Fui and Manase are there, and I'm going to learn everything I can from those guys," Unga said. "Right now, I've got four years left and those guys are upperclassmen and I respect them. I'll give them all the time they need. But I'll work my butt off to get the time I need. I'm going to work my way up there and see what happens. Right now, I'm very confident with what I'm doing. It keeps growing every day."