A brutal hit in the second quarter of Sunday's game against the San Francisco 49ers left Houston Texans quarterback Tom Savage on the ground with his hands trembling.

Savage was allowed to return to the game for one series, then later ruled out with a concussion.

Savage remained on the ground for several seconds after being hit by Elvis Dumervil on a third-down play, struggling to roll over to his side while his hands twitched. He was evaluated by team doctors, according to ESPN, but subsequently allowed to return to the game.

After throwing two incompletions on the ensuing drive, Savage was further evaluated and taken to the locker room. Backup quarterback T.J. Yates replaced Savage and finished out the half, leading the Texans on a nine-play, 75-yard scoring drive.

As he laid on the ground, Savage appeared to exhibit signs of a fencing response, which is generally characterized by the unnatural flexing or extension of the arms after impact to the head.

Savage's return to the game drew widespread criticism on social media from fans, media members and concussion experts like Chris Nowinski, the CEO and co-founder of the Concussion Legacy Foundation.

"I would not let my worst enemy go through the 2017 NFL sideline concussion protocol," Nowinski, who has previously described the league's protocol as a "fraud," wrote on Twitter.

In Week 17 last season, Savage was initially cleared to return to a game against the Tennessee Titans, but he was later diagnosed with a concussion and ruled out.