The San Francisco 49ers Week 9 matchup with the Atlanta Falcons got really weird really quickly. Blaine Gabbert took a big hit early in the fourth quarter, which resulted in a roughing the pass penalty. He was prepared to continue playing, but the NFL's independent neurologist ("concussion spotter") called down to the refs and required they take Gabbert out of the game.
Gabbert went to the sideline to go through the in-game concussion protocol, and Colin Kaepernick replaced him on the drive. Kap handed off on the first play, and then was incomplete throwing to Vance McDonald. The throw was a bit high, but McDonald probably should have hauled it in. After the incompletion, Gabbert was cleared and able to return to the game. There were a mix of boos when Kap came into the game.
Here's the hit that resulted in Gabbert's brief departure from the game. This is exactly why the NFL has an independent neurologist who can remove players from a game. It was a monster hit, and Gabbert was ready to continue playing. The protocol would indicate he did not suffer a concussion, but it made sense to check on it and be safe.