Still, the Dallas Cowboys' first-round pick doesn't have to say much to make it clear that he's confident about being a starting linebacker even though he last played the position as a sophomore in high school.

"Yeah, I feel comfortable," Spencer said.

With growing uncertainty about when veteran Greg Ellis will return from a torn left Achilles' tendon, it seems ever more likely that Spencer will be a rookie starter when the Cowboys play their season opener Sept. 9 at home against the New York Giants.

"I feel like they're counting on me right now," Spencer said Monday. "So I don't think it will change from the season to right now."

Like former first-round pick and Pro Bowl linebacker DeMarcus Ware did two years ago, Spencer is making the transition from college end in the Cowboys' 3-4 defense.

Ellis made the switch last season and had a team-high 4-1/2 sacks when he got hurt in the ninth game.

Playing the first half in the Cowboys' 23-10 preseason-opening victory over Indianapolis, Spencer got credited with only one assisted tackle. But the Colts also didn't really run or throw Spencer's way.

Spencer said he felt comfortable and didn't have any mental mistakes.

Teammates already get a sense of what Spencer can do when blitzing.

"I think he's going to turn out to be a great pass rusher," defensive end Marcus Spears said.

Spencer had 10-1/2 sacks his senior season at Purdue, often bull-rushing around ends or tackles to get to the quarterback.

The advice Spencer has gotten from Ware in making the transition: "It just takes time and reps. You've got to just keep working."

Extra points: Safety Ken Hamlin, who missed the preseason opener after taking a shot to the head during a drill last week, returned to practice Monday.