A high-profile NFL injury has put the spotlight back on football players' risk of concussions, which are linked to head trauma and long-term symptoms. Miami Dolphins quarterback Tua Tagovailoa is on medical leave after getting hurt twice in four days. He may have suffered a concussion Sept. 25 after being tackled, but the team described it as a back injury and he played during the second half. During a nationally televised game a few days later, the 24-year-old from Hawaii was diagnosed with a concussion after his head hit the turf. He left the field on a stretcher after 10 minutes. Coach Mike McDaniel called it a "scary moment."

A concussion (temporary blackout or confusion caused by a blow on the head) can be worsened by rushing back to physical activity. "It's a potentially life-threatening brain injury," says Miami neuroscientist Chris Nowinski, who played football at Harvard University. Athletes can need months or years to fully recover from repeated concussions. That's why NFL policy is to remove and evaluate a player immediately if he reports symptoms or they're seen by a trainer, coach, teammate or assigned observer. Those diagnosed with a concussion must undergo a five-step process before returning. The player must also be cleared by a team doctor and by an independent physician. The outside doctor who was part of the process that let Tagovailoa return to the field was removed. (The quarterback's name is pronounced TWO-uh TUNG-o-vai-LOA.)

The league and its players association now are doing a joint inquiry into how the Dolphins handled the quarterback's first injury. "I am upset and concerned just like any fan — and just like any physician is any time one of our players suffers any type of injury," said Allen Sills, the NFL's chief medical officer. The organization adopted new rules in 2011 about handling concussions and updated them repeatedly amid intense scrutiny and lawsuits by thousands of former players, alleging the league downplayed head injury risks for decades. More than 100 NFL players per year report concussions, with the true number considered to be much higher. "Never assume an NFL team will protect its players," Washington Post sports columnist Jerry Brewer wrote last week. "Never assume infallible protocols are in place."

NFL doctor says: "We're constantly updating and looking to modify the [concussions] protocol as we learn more from our own data and also as we learn more from the scientific community." – Dr. Allen Sills, chief medical officer

Coach says: "All of his teammates, myself, we're all very concerned." – Mike McDaniel, Miami Dolphins

Congressman says: "I pray and hope that the Dolphins and NFL officials did not disregard Mr. Tagovailoa's safety to rush him back into action." – Rep. Bill Pascrell, D-N.J.