"I'm not going to say I'm going to take it easy on you, but I'm not going to try to hurt you," Stills said. "This game is about us, not me."

The increased awareness of concussions hasn't been limited to players.

NFL coaches understand the consequences of pushing players back onto the field after they have incurred brain trauma.

New awareness

In previous generations, a player would be given ammonia capsules on the sideline and rushed back into the game once his head cleared.

Billick compared the attitude toward concussions to the way heat was dealt with at training camps. Coaches once thought they could toughen their players by not giving them water in sweltering conditions.

"Think about it. How stupid was that? But it was from ignorance, not maliciousness," Billick said. "The limit of your medical knowledge back then [for concussions] was, `Just shake it off.' "

Billick said his protocol in handling players with concussions is simple: He doesn't have a say.

When a player suffers a head injury, he said the player's status will be determined by the team doctor and trainer.

"When they tell me a player shouldn't go, it's done and the end of discussion," Billick said.

Pressuring players back onto the field has become a focal point for the NFL after former New England linebacker Ted Johnson said he wasn't given enough time to recover from his head injuries.

Johnson said he suffers from deep depression and an addiction to amphetamines because coach Bill Belichick pushed him onto the field in 2002 against the advice of the trainer.

Belichick responded to the allegation by saying, "If Ted felt so strongly that he didn't feel he was ready to practice with us, he should have told me."

Billick said he doesn't believe that happens these days, adding that a coach "would be criminally liable" if he did.

Said Billick: "I can't imagine the individual that would say, `No, I know more than a doctor or trainer.' "

Risk vs. reward

The trainers and doctors can tell a player he can't return to the game. The coaches can agree with them.

But players sometimes put themselves at risk by sneaking back onto the field.

At every level of football, Tucker has told a player to sit during a game only to have the player return without his knowledge. The trick now is to take the injured player's helmet away.

"You've got someone who is injured and irrational, and that's a bad combination," Tucker said.

In the player's mind, he could lose respect -- or, more important, his job -- by remaining on the sideline.

Now, every player who suffers a concussion has to ask himself if the long-term risk is greater than the immediate reward.

"As a player, you don't ever want to come off the field," Heap said. "There is a reason most guys are out here -- it's because they're pretty stubborn. Since we were kids, we learned how to hit, how to be tough and how to play through things.

"It just changes now when it's the rest of your life that you're dealing with."

Sun reporter Ken Murray contributed to this article.