In the third quarter of the Bears-Packers Thursday Night Football game, with the Packers driving toward the end zone, Green Bay wideout Davante Adams ran across the middle of the field, looking for a routine pass from Aaron Rodgers. He found it, and seconds later Bears linebacker Danny Trevathan found him. Chicago safety Adrian Amos already had Adams wrapped up, but Trevathan soared into the play, lowered the crown of his helmet and slammed into Adams.

The resulting hit was brutal. We’re embedding it below, but with a strong warning that it contains graphic and disturbing imagery.

Trevathan’s hit was so vicious that it forced Adams's mouth guard to shoot into the air. The image of it floating as Adams falls helplessly to the ground is haunting. Immediately, several players from both teams began calling for medical attention for Adams, who laid motionless on the ground. Adams was eventually put onto a stretcher, taken through the tunnel, and sent to the hospital via ambulance. He flashed a thumbs-up as he was taken off the field.

Thumbs up from DeVante Adams as he was being taken off on a stretcher. Good sign. Still brutal what happened. pic.twitter.com/4fTuHMNVuZ — NFL Update (@MySportsUpdate) September 29, 2017

Shortly after, the Packers released an update:

Adams is conscious and has movement in all his extremities. He's been taken to a hospital for further testing. — Green Bay Packers (@packers) September 29, 2017

While Adams’s injuries have yet to be diagnosed, it’s worth noting that, in a refrain all too familiar to players who have made it to the NFL, Adams has a history with concussions. His only reported concussion came in October 2016, after he took a hit in a game against the Dallas Cowboys. Initially, he told reporters that he didn’t have a concussion, but he was then put through the protocol before returning four days later to play in another Thursday Night Football game. In July, Adams also partnered with one of his former Pop Warner coaches to create a tool to help screen for concussions in youth football games.

In March, the NFL approved automatic ejections for “egregious hits to the head.” Yet although Trevathan received an unnecessary roughness penalty, he was not ejected from this game, and he played on the very next snap, a 4-yard touchdown pass to Jordy Nelson. Trevathan could be suspended for the hit, but that doesn’t change the unconscionable nature of the act or lack of an immediate ejection, especially given the current conversation about hits to the head and brain injuries in football.

The NFL has had a problem with head trauma for virtually its entire existence, and has been unable to avoid the controversy in recent years. The concussion protocol was instituted in 2009. In July, Boston University discovered CTE in 110 of the 111 brains of NFL players it studied. On Tuesday, BU announced that it is moving closer to finding a way to diagnose CTE in living patients. If those researchers are correct, the findings from such a development could eventually spell the end of the NFL if young athletes—or current NFL players—decide the sport is too violent to pursue or potential fans tune out rather than face a moral reckoning every time they turn on a game.

On Thursday night, the league, fans, and players got a sickening reminder of why that research is necessary. Because if football doesn’t fix its head trauma problem, the sport is surely doomed.