LOS ANGELES -- The NFL's concussion protocols were back in the spotlight on Friday after an injury to Miami quarterback Tua Tagovailoa that sent shockwaves rippling through America's most popular sport
Dolphins star Tagovailoa was stretchered off the field during Thursday's televised primetime loss to Cincinnati after suffering a violent blow to the head in the second quarter.
The alarming incident occurred just four days after Tagovailoa appeared to sustain a concussion against Buffalo.
In that game, Tagovailoa could be seen shaking his head after his helmet hit the turf before collapsing as his legs buckled.
However, he was given the all clear to return, with team officials later saying he had suffered a back injury.
That decision -- and the decision to allow him to suit up against Cincinnati on Thursday -- faced fierce scrutiny on Friday.
J.C. Tretter, the president of the NFL Players Association, which has launched an investigation into how Tagovailoa was evaluated on Sunday, called for changes to the concussion protocols.
"We are all outraged by what we have seen the last several days and scared for the safety of one of our brothers," Tretter said.
NFL protocols list certain symptoms as evidence of concussion which are deemed "No-Go signs" and should lead to a player being removed immediately from the field of play.
These include loss of consciousness, confusion, amnesia, and gross motor instability.
- NFL investigation -
Tretter said Tagovailoa's stumbling against Buffalo was a clear "no-go" sign that should have seen him withdrawn from the field.
"What everyone saw both Sunday and last night were 'no-go' symptoms within our concussion protocols," Tretter said. "The protocols exist to protect the player and that is why we initiated an investigation.
"Our job as the NFLPA is to take every possible measure to get the facts and hold those responsible accountable.
"We need to figure out how and why the decisions were made last Sunday to allow a player with a 'no-go' symptom back on the field."
As part of the NFL's concussion rules, unaffiliated neurotrauma consultants (UNCs) are on the sidelines at each game to check for signs of concussion amongst players.
However NFL rules also state that "the responsibility for the diagnosis of concussion and the decision to return a player to a game remain exclusively within the professional judgement of the head team physician."
The NFL's chief medical officer Allen Sills said Friday the league was still gathering information as part of its investigation into how Tagovailoa's injury was handled.
"I think we have to go through the data and speak with everyone involved and understand exactly what they saw and what they heard and whether they correctly applied the concussion protocol," Sills told NFL Network.
"The purpose of that review is to make sure that the protocol was followed. There are very serious consequences if the protocol was determined not to have been followed."
- 'It does look fishy' -
Experts said they expect investigators to drill down on how Tua's stumbling against Buffalo was deemed a back injury rather than a neurological issue.
"I'm curious to see what comes out of the investigation, how they determined that the gross motor instability was from a back injury and not a concussion," said Rachael Hearn, an athletic trainer and researcher into chronic traumatic encephalopathy (CTE), the degenerative brain condition caused by blows to the head and associated with contact sports.
"I don't want to speculate because I don't know what other symptoms were there," Hearn told the GridIron podcast. "It does look fishy though."
"I hope for everyone's sake, they have really good documentation and notes regarding the decision they made that day, particularly in allowing him to return to the game.
"Had it been me, I would probably have taken him off for the game."
Chris Nowinski, the chief executive of the Concussion Legacy Foundation, a non-profit which provides support to athletes, veterans and others affected by concussions, had warned against Tagovailoa playing on Thursday, saying it was a "step backwards".
On Friday, Nowinski said Tagovailoa had been let down by the Dolphins staff.
"The Dolphins and teams alike are trying to get away with situations like these all the time," Nowinski told Fox Sports Radio.
"All we're doing is watching our heroes die way too young, and it's a shame.
"If I was Tua, I wouldn't come out to play for the Dolphins ever again."
The NFL has faced intense scrutiny over the past decade over concussions and head trauma.
In 2015, the league agreed to a $1 billion settlement to resolve thousands of lawsuits by former players suffering from neurological problems.
© Agence France-Presse