Fans and media members alike can point to distinct moments in the recent history of the NFL and the NHL when the leagues were confronted with concussion issues, and those instances may have changed the course of concussion awareness in their respective sports.

For the NFL it was week 6 of the 2010 season, when DeSean Jackson, Chris Cooley and Josh Cribbs each suffered a concussion after brutal hits by defenders. That prompted Sports Illustrated to put the issue on its cover with an article titled "The Hits That Are Changing Football." It didn't take long before the NFL increased penalties for hits to the head.

A few months after the NFL's infamous October weekend, the NHL's marquee player, Sidney Crosby, suffered two concussions in the span of one week. The Pittsburgh Penguins center and likely MVP sat out the rest of the 2011 season and most of the 2012 season.

The inconsistencies in Crosby's diagnosis and the widespread mystery surrounding his condition were reminders of just how little is understood about head injuries. Just as the injuries to Jackson, Cooley and Cribbs changed the culture of hits in the NFL but did not resolve the problem, Crosby's injury has raised awareness in the NHL, but the league still has a long ways to go when it comes to dealing with these injuries. For the record, the NHL is still well behind the NFL in this regard, as some of hockey's highest executives are still dismissing the issue by saying research is inconclusive.

Now it appears that a third professional sporting league, NASCAR, is entering a phase that will likely change the way it approaches concussions. One of the sport's most popular drivers, Dale Earnhardt Jr., suffered two concussions over the past six weeks and as a result has missed consecutive races. Another top driver, Denny Hamlin, said he felt dizzy and had his "bell rung" after a crash during testing Thursday at Kansas Speedway.

Fixing the problem will require more work in NASCAR than in either the NFL or the NHL. Not only is it harder to determine when a NASCAR driver has suffered a concussion (the drivers are hidden in a car so it is almost impossible for spectators to see the injury), but there is no protocol for drivers after suffering a concussion. Earnhardt did not seek medical attention after his Aug. 29 concussion, and it was only after another head injury on Oct. 7 that he decided to visit a doctor.

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In the wake of Earnhardt's injuries, several high-profile drivers have issued disturbing responses when asked whether they would seek medical attention under similar circumstances.

"Honestly, I hate to say this, but no, I wouldn't [seek medical attention]," said Jeff Gordon. "That's why I say we all play a part in this. If I have a thought at the championship, there's two races to go, my head is hurting, and I just came through a wreck, and I am feeling signs of it, but I'm still leading the points, or second in the points, I'm not going to say anything.

"I'm sorry. You know, that's the competitor in me, and probably many other guys. And, that's to a fault. That's not the way it should be. It's something that most of us, I think, would do. I think that's what gets a lot of us in trouble."

Whereas football or hockey players are part of a team, and therefore sitting out won't disqualify the entire squad, if a NASCAR driver like Earnhardt has to miss several races, that could be a death sentence for his championship hopes. Before suffering his crash on Thursday, Hamlin admitted that, depending on where he was in the standings, he might not have made the same decision as Earnhardt.

“If I was in my position, I’d probably hide it," Hamlin said. “I’d race on, or at worst, I’d run a lap, get the points, get out and let someone else do it."

In the wake of Earnhardt's concussions, NASCAR officials have said they are looking into increased testing for their drivers. Perhaps the most logical next step is baseline testing for drivers as part of a regular preseason physical.

“We are always evaluating and reviewing our policies and procedures, especially when it comes to safety,'' NASCAR spokesman Kerry Tharp said. "We will continue to work closely and review our policies with the medical experts that advise NASCAR on baseline testing and other medical issues.

"While not mandatory, baseline testing can and has been used and is just one of the many tools a neurologist or neurosurgeon may use as part of a neurological assessment.''