In the moments before and after Miami Dolphins quarterback Tua Tagovailoa was taken away on a stretcher, his younger brother, Taulia, kept trying to call his mom. There was no answer. Their parents, Diane and Galu Tagovailoa, were at the Dolphins-Bengals game in Cincinnati. Taulia was 500 miles away and needed someone to tell him Tua was OK.

Like his brother, Taulia is a football player, but what he had just seen scared him -- Tua spun around and violently flung to the turf, smacking the back of his head on the ground. He remained on the Bengals' logo, with his forearms raised and his fingers stiffened in a contorted position near his face.

It was Thursday night, Sept. 29, more than three months before Buffalo Bills safety Damar Hamlin would lie on the same field in Cincinnati while a team of medics rushed to resuscitate him and help save his life. On both nights, everything eerily stopped. The game eventually went on the night of Sept. 29, but Taulia Tagovailoa, the starting quarterback for the University of Maryland, had a walk-through practice the next day and a game against Michigan State to prep for and all he could think about was finding a flight, immediately, to see Tua.

He tapped his mom's number again, and again, and started to cry. "It just looked really bad," he said.

When Diane Tagovailoa answered, she said Tua was with the doctors and had to be rushed to the hospital. His father eventually got on the phone and told Taulia to focus on Michigan State. But he barely slept that night. On his way to the Terrapins' team hotel the next day, he received a FaceTime call from his brother. Tua was smiling.

In an effort to allay his brother's fears, Tua, 24, recited his name, birthday and other basic information. He joked that he didn't have a concussion. But by then, he had hit his head on the ground twice that last week of September; the first was not reported as a concussion, the second one was. He'd be the impetus for an investigation by the NFL and NFL Players Association into how he was cleared to play, which prompted changes in the league's concussion policy.

On Christmas Day against Green Bay, Tagovailoa suffered another concussion, and he hasn't played since. Miami's fortunes have risen and fallen on the back of Tagovailoa, whose transformation in his third year prompted chants of M-V-P and faraway thoughts of a Super Bowl. With Tagovailoa, the Dolphins are 8-4 in games he's finished and 1-4 without him. His passer rating leads the NFL (105.5), ahead of Kansas City quarterback Patrick Mahomes (105.2).

So naturally, a long-suffering fan base hung on every injury report and update from coach Mike McDaniel this week as the Dolphins prepared for Sunday's wild-card matchup at Buffalo, their first playoff game since 2016. On Wednesday, McDaniel said Tagovailoa still hasn't been cleared to practice, and won't play this weekend.

McDaniel called it "frustrating" for Tagovailoa, who celebrated with his teammates in the tunnel Sunday after the Dolphins, playing with rookie quarterback Skylar Thompson, eked out an 11-6 playoff-clinching victory over the New York Jets. McDaniel said it was a big goal for Tagovailoa to get his team to the playoffs, and play in them.

But take away the ambiguity in Week 3, in which Tagovailoa was listed with a back injury in the Buffalo game, and his status this week -- and next week should the Dolphins pull out the upset -- might not even be in question. Two renowned concussion experts told ESPN that Tagovailoa's head trauma during the Bills game had the appearance of a concussion. Dr. Julian Bailes, chairman of the department of neurosurgery at NorthShore University Health System, said that's significant because three concussions in a finite period is generally the threshold that requires a player to be held out for an extended amount of time, possibly months. If Tagovailoa has had three concussions, Bailes believes he should sit.

"The brain doesn't know whether it's the playoffs or not," he said. "The brain doesn't appreciate what part of the season you're in. It needs to recover."

ON SEPT. 26, the day after Tagovailoa hit his head on the ground during the Bills game, Dr. Chris Nowinski was in rural Nebraska telling the widow of former Harvard teammate Chris Eitzmann that her husband, who died in 2021 of alcohol poisoning, was found to have had CTE. In the years since Nowinski co-founded Boston University's Chronic Traumatic Encephalopathy Center, he has had many conversations like this. But this time, he was trying to explain to Eitzmann's 14-year-old son why his dad wasn't there anymore.

It had been a long week for Nowinski, vacillating between sadness and anger. He fired off three tweets during and shortly after the Dolphins-Bills game, calling the back-tweak diagnosis "bull$hit."

Tagovailoa had been pushed to the ground in the second quarter against the Bills and hit his head. He got up on his own, shook his head, staggered and temporarily had to be propped up by two teammates. But he returned to the game after halftime and led the Dolphins to a 21-19 victory. Tagovailoa told medical staff he aggravated a back injury on the play. Although Miami never ruled the injury a concussion, Nowinski told ESPN he believed that it was.

On Thursday, Sept. 29, a few hours before the Bengals game, Nowinski tweeted, "If Tua takes the field tonight, it's a massive step back for #concussion care in the NFL. If he has a 2nd concussion that destroys his season or career, everyone involved will be sued & should lose their jobs, coaches included. We all saw it, even they must know this isn't right."

Tagovailoa played that night in Cincinnati and later would say he was knocked unconscious. His hands were in a modification of the fencing response position -- automatic movements of the body that occur from impact. His cousins were so affected by the scene that it prompted a group chat among about 15 people, including their spouses, and they worried and prayed for him.

After Tagovailoa's concussion in Cincinnati, Miami reached out to Bailes. The Dolphins were examining how they should proceed with their quarterback, and Bailes said he was one of a small group of doctors contacted.

Bailes, a member of the NFL's Head, Neck and Spine Committee and the NFLPA's Mackey-White Health and Safety Committee, was a Pittsburgh Steelers team doctor during the latter part of the career of center Mike Webster, the first player Dr. Bennet Omalu diagnosed with CTE. Research from Omalu and Bailes eventually forced the NFL to rethink its policies on players' health and brain safety.

Bailes said that he didn't examine Tagovailoa and that he believes the Dolphins handled the Cincinnati concussion properly in sitting the quarterback from Sept. 30 to Oct. 22. In all three of Tagovailoa's blows to the head, Bailes said that the mechanisms of injury were "very similar" in that he was thrown to the ground and hit the back of his head. Because he fell backward, he couldn't break his fall.

On Oct. 1, the NFLPA fired the unaffiliated neurotrauma consultant involved in the decision to allow Tagovailoa to return to the Buffalo game. Multiple sources said the firing came after it was found the consultant made "several mistakes" in his evaluation. A week later, after its joint investigation with the NFLPA, the league added "ataxia" to its list of symptoms for which a player cannot return to a game. Ataxia is defined by the National Health Service as a group of disorders that affect coordination, balance and speech.

Nowinski said there is a growing awareness that hits to the head occurring close together in time are "riskier" for long-term issues. He also said studies show that with each concussion the odds of having another one increase.

"Why we think that happens includes what they call the neurometabolic cascade, the chemical and metabolic changes that occur with a concussion," Nowinski said. "Once they're triggered once, it may require a slightly lower threshold to make that happen again. Your brain's resilience may be diminished in the sense that you've got 86 billion or so neurons and trillions of connections between them, and when you get a concussion, you lose some, but it's not enough to permanently impair you.

"But if neurons die, if axons are severed, they don't come back. And if you just keep taking some away with each concussion, eventually your brain can't overcome the damage and the [ability to recover] becomes diminished."

TAGOVAILOA'S FORTUNES, at least from a football perspective, changed with one call on Feb. 7, 2022.

McDaniel had just been named head coach of the Dolphins and was flying from the West Coast to South Florida when he FaceTimed his new quarterback from the plane. McDaniel told Tagovailoa that he knew he had the ambition to be great and that his job as coach was to get all that greatness out of him.

"I'm going to make sure that when you look back at this day, you're going to be like, 'Damn, that was one of the best days of my career, too,'" McDaniel told him.

Tagovailoa, the Dolphins' fifth overall pick in the 2020 draft, had been widely considered a bust up to that point, so much so that in 2021 Miami considered pursuing and did due diligence on Deshaun Watson amid civil litigation alleging sexual assaults. This past August, an NFL investigation concluded that Dolphins owner Stephen Ross and minority partner Bruce Beal had violated the league's anti-tampering policy on three occasions, from 2019 to 2022, in conversations with quarterback Tom Brady and the agent for then-New Orleans Saints coach Sean Payton.

Brian Flores, the Dolphins' coach at the time, had a chilly relationship with Tagovailoa. Flores was defensive-minded and known for being intense. In close games, he would bench Tagovailoa in favor of veteran Ryan Fitzpatrick.

Mike Locksley, Tagovailoa's offensive coordinator at Alabama, said Tagovailoa is a people person who doesn't necessarily operate well with dysfunction.

"Not that you can't jump his butt. I've seen times when coach [Nick] Saban would get after him," said Locksley, now the head coach at Maryland. "He's not hard to coach. He wants to please his coaches and please his teammates, almost to a fault, where he'll put someone else above himself."

McDaniel was seemingly the anti-Flores -- loose, funny, nerdy and oozing with positivity. Tagovailoa didn't know how to respond to it at first and proceeded with cautious optimism. But McDaniel inspired him to work harder and be better.

The 2022 season began, essentially, in a park near Tagovailoa's house in South Florida. It was summer. Tagovailoa's receivers met their quarterback, some in shoulder pads and helmets, for workouts that stretched as long as 2½ hours in the punishing heat. Tua Tagovailoa's brother, Taulia, trained with them and could sense the chemistry building.

The Dolphins had just added All-Pro receiver Tyreek Hill and top free-agent tackle Terron Armstead in the offseason in part to build a support system around their quarterback, and there was Hill, formerly a favorite target of Mahomes', in that heat, on Tagovailoa's turf, running routes.

The first game of the season inspired hope, a 20-7 win against the New England Patriots. But Miami fans have seen hope wane through more than a dozen quarterback failures in the lost decades post-Dan Marino. Skepticism was a given.

All that eroded in Week 2. Tagovailoa put together a six-touchdown, 469-passing-yard performance, rallying his team from a 21-point fourth-quarter deficit in a victory over Baltimore that made the Dolphins 2-0 and brought hysteria that Tagovailoa wasn't just their franchise quarterback -- he was going to take them to places they hadn't been since the 1980s. "That was f---ing awesome," Marino said after the comeback.

But every high seemingly came with a subsequent low of equal value, and the Buffalo win the next week was met with the reality of Tagovailoa's first head injury.

Miami would win five games, then go on a five-game losing streak. It would go to Buffalo on Dec. 17 and nearly beat the Bills in frigid temperatures, then, just when it appeared as if the Dolphins were back on track, would lose Tagovailoa to another concussion in a home loss to Green Bay.

In the first half of that game, he was tackled after a throw and fell and hit the back of his head. He got to his feet and did not leave the game. He threw three interceptions in the fourth quarter. McDaniel told reporters that the Dolphins reviewed film from the game and saw things that "caused them to prod" Tagovailoa. After further discussion and observation of him Monday after the game, they advised him to visit with team doctors, and he was placed into the concussion protocol.

It prompted another investigation by the NFL and the NFLPA, which concluded that concussion protocols were not violated because Tagovailoa didn't exhibit visible signs of a concussion during the game.

Tagovailoa has eschewed one-on-one interviews this fall, saying he wanted his play to do the talking. When healthy, it has. He threw for 3,548 yards and 25 touchdowns despite the chunks of season taken away by concussions. He completed 64.8% of his passes, with three of his eight interceptions coming in the fourth quarter of that Green Bay game.

Vinny Passas, his high school quarterback coach at Saint Louis School in Hawaii, was in the middle of a training session Dec. 26 when an alert popped on his phone that Tagovailoa had suffered another concussion. He said he couldn't remember seeing Tagovailoa endure as many setbacks and challenging moments as he has in 2022.

He knows how hard it must be for Tagovailoa to sit. Passas has coached high school football in Hawaii for more than 40 years, and mentored quarterbacks such as Marcus Mariota and Timmy Chang. In Polynesian culture, Passas said, a mentality of toughing it out and playing through injuries is deeply ingrained.

"I remember coaching in a Polynesian Bowl game where a quarterback took himself out after a hit," he said. "At halftime, a couple of Polynesian players told him, 'Gosh, if we did what you did by taking your pads off and not playing the second half, our parents would come down here and give it to us because we'd be, like, embarrassing our family like that.'"

Tagovailoa's parents did not respond to interview requests for this story. In an interview with Maria Taylor for "Football Night in America" in late October, as Tagovailoa returned from his Cincinnati concussion, he said that his injuries had been "a little tough" for his parents. He also acknowledged to reporters that week that he's always been a quarterback who opted to try to make something happen, who'd wait for receivers to get open instead of throwing the ball away. But he was learning, he said, and was now thinking about his longevity.

His first game back against Pittsburgh, he tried to bulldoze defenders, twice.

Adam Amosa-Tagovailoa, a former offensive lineman at Navy who is Tua's cousin, said that when they were children and needed to be reminded to never give up, their grandfather Seu would tell them about the story of the lion and the gazelle.

"The gazelle wakes up running away from danger," Amosa-Tagovailoa said, "while the lion wakes up hungry, always starving, trying to get to the next meal."

IN THE END, McDaniel's positive vibes and Tagovailoa's spurts of brilliance could not withstand an offseason inevitability: Tua's future in Miami is once again murky. The Dolphins have until May to decide whether to exercise his fifth-year option.

Will they sign Tagovailoa to a long-term extension after a year in which he has proved he is capable of high-level play but also with durability issues a concern? Tagovailoa was considered an injury risk in the 2020 draft because his college career at Alabama ended when he took a sack and dislocated his right hip, also fracturing its posterior wall, and suffered a concussion and a broken nose.

"You can't tie the money to a player you're not sure can stay healthy," an AFC exec told ESPN. "If he didn't have the medical history, maybe you think harder about doing something. The concussion dynamic is harder to figure out since I'm not sure his medical on that.

"The Dolphins are in a tough spot, because he's a good player but a lot like Kirk Cousins. If you give him good football players, he's going to be productive. If you ask him to go win a game and put a team on his back, that's asking a lot."

Despite all the hits in 2022, Nowinski, a neuroscientist who co-founded the Concussion Legacy Foundation, said he does not consider Tagovailoa to be concussion-prone. He said that's a subjective label given to people who have had multiple concussions over many years. But he is worried that NFL teams might label him that to justify paying him less or not giving him as many opportunities.

"I'm highly concerned that he will get that label, and not fairly," Nowinski said. "I would look at it as he had one concussion, which happens. He then receives an improper diagnosis and care and received what is either a second concussion or a hit that exacerbated the first. But either way, it left him susceptible for months to a future hit, causing another concussion, more susceptible than he had been prior, which is, I think, what we saw.

"None of this was his fault. He's been playing football for a long, long time and never had these issues. ... We need to give him time to properly recover before he should be given any labels."

The NFL does not share concussion tracking information during the season but provides injury data at the end of each season. In 2021, there were 187 reported concussions in the regular and preseason combined. This year, the league has conducted three investigations into the application of concussion protocol -- one with New England receiver DeVante Parker and two with Tagovailoa.

Tagovailoa's agent is Leigh Steinberg, who for decades has represented the top quarterbacks in the NFL, from Steve Young to Mahomes. Steinberg is known for being at the forefront of player safety in regard to brain injuries long before football acknowledged them. Steinberg was holding seminars to educate his players on the long-term effects of concussions as early as the 1990s. He declined to comment for this story.

In an interview in November, Taulia Tagovailoa said he was "really nervous" to watch his brother play in his Week 7 return against Pittsburgh. He didn't know how he'd play or move. But he said Tua didn't skip a beat, and that gave him comfort.

There are decisions to be made by the Dolphins, and by Tagovailoa. He and his wife, Annah, became parents this year. When asked what was the difference in his brother's game this season, Taulia cited chemistry, then thought about it some more. The biggest difference, he said, is that Tua has a son, and that motivates him and helps him block out everything else.

"I think his son really changed his life," Taulia said. "When he comes home, it's bigger than football. It's your son. You always want to be good for him. You always want him to grow up and say, 'That's my father.'"

ESPN's Jeremy Fowler contributed to this report.