SAN FRANCISCO -- The video of Alex Smith smashing into Rams linebacker Jo-Lonn Dunbar replayed several times on Bay Area TV screens Sunday afternoon as the 49ers' medical staff tested the quarterback for signs of a concussion, confirmed their suspicions and then escorted him off the field.

That tackle, so fierce at the moment of impact, seemed the likely culprit. Smith played 12 more downs after the hit, showing no obvious signs of wooziness and throwing a touchdown pass before he went to the sideline as a matter of course. He reported blurred vision once he got there.     

Jim Harbaugh would say later that the doctors had not identified the 4-yard run right into Dunbar as the cause of Smith's concussion. "From what I've been told by the doctors and trainers, it seems like it was the quarterback sneak,'' the coach said, referring to a 4th-and-1 conversion that happened exactly five plays after the big hit and six before the touchdown pass.

Smith will now go through specific testing protocols to determine when he can practice and play again. So will two of his quarterback peers, Michael Vick and Jay Cutler, each knocked out of action by a concussion on Sunday.

The NFL has every incentive, from pending litigation to the maintenance of its preeminent position in the family-entertainment spectrum, to perfect the prompt detection and treatment of brain trauma. But the uncertain way Smith's concussion revealed itself only emphasized the imprecision of the science and the elusiveness of that goal.

After the game, it was odd to hear his 49ers' teammates alternate between discussing their confused emotions about participating in the NFL's first tie since 2008 and explaining how little they knew about Smith's concussion during the game.

"I just heard about it; a reporter told me,'' center Jonathan Goodwin said. "When he went out, I thought it was something else, maybe he hurt his eye.''

Left tackle Joe Staley, a longtime friend of Smith's, said he sensed nothing wrong with the quarterback during his final plays of the game and didn't know he was hurt until Colin Kaepernick came in at quarterback for the next series. "The flow of the game is so fast, you don't really have time to check if a guy's OK,'' he said. "I didn't notice anything, but I wasn't paying attention. I was just thinking about the play-calling.''

Over in another corner of the locker room, safety Dashon Goldson was holding forth half-comically on how he didn't know that ties were possible. "When I saw everybody walking onto the field, I was like 'Where's everybody going?''' he said.

Goldson wasn't alone. Rams receiver Danny Amendola told NBC's Peter King that he thought the 24-24 game would head into another overtime period. When Donovan McNabb said he thought the same thing four years ago, the remark set off howls of derision. Given that he was a quarterback, responsible for the pace and urgency of an offensive possession, McNabb may have deserved a lot of the mockery. But Goldson seemed to be mocking the idea of accepting a tie. He sounded more disappointed than clueless, as if he found it a violation of every football instinct he had ever cultivated to leave a field without clear resolution.

Most players live in that kind of haze every Sunday, blocking out every thought, every sense, except the ones that can earn them a win. The line between consciously choosing to ignore something as monumental as a brain injury, to play the tough guy, and genuinely not noticing is … well, who knows where it lies?

Smith couldn't explain it on Sunday evening. The NFL protocol, the 49ers said, prohibited them from making a concussed player available for interviews. If that represents an attempt at evasion, so be it. It's also progress.

Thirteen years later, it's shocking to remember that Steve Young appeared in a media tent outside Sun Devil Stadium after an unblocked blitz by Aeneas Williams left him prone on the field, motionless for several seconds. Young, whose head had also been battered a week before, would never play professional football again. Doctors wouldn't clear him for the rest of the 1999 season, and he retired before the 49ers' 2000 training camp.

Even then, watching him stand up and answer questions that night in Arizona, despite a concussion diagnosis, felt strange. Today, knowing what we've learned about brain trauma in recent years, it would seem obscene.

In the hours after his final game, Young seemed weary but very much like himself. Several other times in his career, reporters had gathered around him shortly after he had sustained a concussion. Generally speaking, there was no way to tell the difference between his responses then and the exhausted reactions of players who, for example, went through 75 minutes of pro football and didn't achieve a clear outcome.

"I don't really know how to feel,'' Rams linebacker James Laurinaitis said of Sunday's tie. "It's like a numbing feeling.''

The TV cameras caught a telling scene between Smith and Harbaugh just before the quarterback took a seat and a trainer hid his helmet. Smith looked pained. He may not even know which blow caused the concussion. There might not have been a single one. The most updated research suggests that hits known as "sub-concussive events'' have a cumulative effect. Smith took the blow from Dunbar, then absorbed a sack, then ran the sneak within six plays. Then he completed three straight passes for 37 yards and a touchdown.

We can call that remarkable or tough or what it really is -- terribly ominous. The fog around these injuries won't part easily.

For every bit of progress in the culture of sports -- Green Bay's Donald Driver telling teammate Aaron Rodgers not to go back into a game last year because he'd be putting life after football at risk -- there is a countervailing piece of ignorance. Last week, Hornets coach Monty Williams ripped the NBA policy on resting concussed players by saying: "Now, they treat everybody like they have white gloves and pink drawers.''

But bold stubbornness is nothing compared to the subtler complications of identifying brain trauma. The sports media will spend a good part of the next week wondering whether Cutler and Smith will be able to play against each other in the Monday Night Football showdown of Nov. 19. Each of them could have several lower-profile teammates with cumulative head trauma that lingers below the detectable levels, caused by the constant car-wreck banging that constitutes a lineman's job.

So much of the trouble is less dramatic than that collision between Smith and Dunbar on the 4-yard run. It looked like the obvious suspect Sunday afternoon. It really did. Upon review, the tie offers clearer answers.