On Sunday, a bad day for NFL quarterbacks, the Eagles' Michael Vick, the 49ers' Alex Smith and the Bears' Jay Cutler left games with concussions and did not return. In the cases of Vick and Smith, the concussions were the results of the accidental, even incidental, contact that is inevitable in a game of collisions. With Jay Cutler, however, the contact was premeditated and vicious in its design and execution. We saw the beast of football, off the leash.

Let's first make clear what a concussion is. You've read it a thousand times, but a thousand and one times is a thousand too few. A concussion is an injury to the brain. The brain is a gelatinous mass so vulnerable that it is encased in a protective bone, the skull. If that bone is struck, the brain inside moves. The greater the blow, the greater the distance the brain moves, the greater its speed. When the brain crashes against that bone, it can be bruised, it can be ripped, it can bleed. It dies, cell by cell. You've seen fighters. You've seen Joe Louis and Muhammad Ali. You know about the old Bears' quarterback, Jim McMahon, who has admitted to symptoms of early-sign dementia.

Let's make clear, too, that the NFL is in the midst of a concussion crisis that threatens the league's integrity and its bank accounts. More than 3,000 players are plaintiffs in lawsuits claiming the league misled them on the dangers of head injuries. These suits could cost the league billions of dollars. What happened to Jay Cutler on Sunday night was a stark, terrifying example of the NFL's safety problem.

It was late in the first half. It was raining and windy in Chicago. Defense would decide the winner of a game matching teams with 7-1 records. The Texans led, 10-3, when Cutler, back to pass, moved forward out of the pocket. He ran toward the line of scrimmage, tentatively, not certain if he would throw or run.

Here came Texans linebacker Tim Dobbins, a quick, strong 245-pounder. He sprinted straight at Cutler. It was just the two men, isolated near midfield, no other player within 10 yards. No matter what Dobbins would say later -- we'll get to that -- he knew what he was about to do. In the macho vernacular favored by football players everywhere, he was about to "blow up" Cutler. He didn't need to. He could have avoided what happened. He could have thrown himself at Cutler's knees. Or at Cutler's belt. Or at Cutler's number, 6.

But if you're a journeyman linebacker who in seven seasons has moved from San Diego to Miami to Houston, you don't keep your $700,000-a-year job by being invisible. His position coach, Reggie Herring, says Dobbins "possesses a knockout punch." The linebacker is proud of that. He was quoted on the Texans' team website saying, "It's definitely something good to have. Obviously, if you get the opportunity to hit a running back or receiver, you don't want them to fall forward. You want them to fall backwards, because it comes down to the inches."

So, at full speed, locked on a quarterback looking past him and downfield, Dobbins delivered a helmet-to-helmet blow against the defenseless man. More accurately, it was helmet-to-face mask. Dobbins' blow twisted Cutler's helmet from right to left. From a standing-tall position, moving forward to throw a pass, the quarterback was flipped backward, his feet in the air, landing on his back. It was as if he had taken a shotgun blast in the face.

Even as Cutler waited for the next snap, he was dazed. He turned his head fully to the left, once, then a second time, seeming to test the moving parts. It was third-and-9 at the 50, a passing down, and when Cutler couldn't find a receiver, he scrambled past the line of scrimmage. Rather than go into a quarterback's self-preserving slide, Cutler dove head-first toward a defender to get 11 yards and a first down.

That was dumb. It was foolhardy. It also may have been a symptom of how badly his brain was hurt. Yet, astonishingly, Cutler's run was celebrated on national television. NBC's analyst, Cris Collinsworth, said Cutler showed that he was now, if not before, "a real Bears quarterback." Collinsworth must have had two thoughts working. Two seasons ago, Cutler was criticized for sitting on the sidelines during a playoff game after a knee injury. Also, Collinsworth bought into the stereotype of the Bears as Monsters of the Midway, grit and guts, every man tougher than shoe-leather steak. It was macho bullfeathers. Better if Collinsworth had thought of Jim McMahon before celebrating any quarterback putting his brain in harm's way. 

Two plays later, Cutler threw an interception. For reasons unexplained, he had been allowed to finish out the half. He had run for 19 yards (sliding that time) and completed 1 of 3 passes for four yards. At halftime, the Bears finally figured out that he had suffered a concussion. He didn't play again.

All this happened on a day that started with talk about it happening. The Chicago Tribune columnist David Haugh reported that the Bears president, Ted Phillips, spent an hour in a Soldier Field interview room on a panel "designed to show the organization's commitment to concussion awareness." An Army general and two former Bears players detailed "ways the NFL and U.S. Army will join forces to 'change the culture' regarding brain injury."

Perhaps the Bears and the NFL could show the video of Tim Dobbins blowing up the defenseless Jay Cutler. They could even use Dobbins' words to show how today's players still don't get it. Brad Biggs of the Tribune quoted the happy linebacker: "It was good that he was out. You always wanted to take the quarterback out of the game."

But Dobbins insisted that he didn't mean to do it. "I hit him in the chest. I did not hit him in his head. Nowhere near."

The Chicago Sun-Times blogger Sean Jensen quoted a Dobbins explanation: "I just felt like he was going to take off running with the ball and I thought he was past the line. I did not hit him in his head. And, actually, he did. He ran into me. How 'bout that?" Dobbins went on: "I thought it was a bad flag because I really didn't even hit him, nor did I lead with my head."

Everyone else with eyes saw it differently. The Texans were penalized 15 yards for unnecessary roughness. Using the necessary euphemism, referee Gene Steratore called the violation a "hit above the quarterback's shoulders." Without losing much in accuracy, Steratore could have described the hit as an attempted decapitation. The penalty should not have been 15 yards but 30, plus ejection from the game, followed, two days later, by a multiple-game suspension and a fine large enough to get every head-hunter's attention.