Playing surfaces, equipment, rules, and long-standing traditions are being adjusted or eliminated in the rush to grapple with concussions, the disruptions and dangers they create, and - not insignificant - with the lawsuits they generate.
The response has been so swift and widespread, the lawsuits so plentiful, that many fear the issue could soon pose a threat to some sports' continuing to exist.
"I do worry that the intense focus - and, in some cases, overreaction - regarding the presumed risks could threaten the existence of some sports," said Jeffrey Kutcher, a Michigan neurologist who advises the NFL, NHL, and NBA on concussion issues.
Nowhere has the reaction been more noteworthy than in the NFL, which faces legal action from thousands of ex-players in a federal suit being argued in Philadelphia.
"We've been working on this for a long time," commissioner Roger Goodell said earlier this year when it was suggested his league's much-publicized response might be lawsuit-driven. "We've funded research going back into the '90s - well before any of that litigation. This is being done to . . . make our game safer and make other games safer."
The world's most successful sports league has stiffened head-hunting penalties, greatly reduced the high-speed chaos of kickoffs, and mandated extreme medical caution for concussed players.
Other changes, however, aren't nearly as visible.
Since late 2011, certified trainers - paid by the NFL and approved by the players association - have scrutinized every play on press-level TV monitors. Their sole mission is early detection of head injuries such as those that, two Sundays ago, sidelined three high-profile quarterbacks - the Chicago Bears' Jay Cutler, the San Francisco 49ers' Alex Smith, and Vick.
The league also has invested nearly $100 million in safety-related equipment research. The Tom Swiftian results, none of which have yet been adopted, include sensor-equipped mouth guards and helmets with accelerometers that gauge the impact of collisions and instantly transmit the data to officials and trainers.
Concussion concerns are even pushing baseball, that most hidebound of sports, toward radical change. One proposal being considered would provide catchers with quarterback-like rules protection, in the process eliminating one of the game's most exciting and trademark plays, the runner slamming into the catcher at home plate.
In basketball, where hardwood floors can be a hazard, NBA teams are installing more yielding subsurfaces beneath the gleaming maple. In hockey, NHL clubs have replaced the tempered glass surrounding their rinks with softer plexiglass. And in soccer, a few pioneers are wearing helmets designed to lessen the jolt of headers.
The epidemic's repercussions extend beyond the professional level. Forty-two states, including Pennsylvania, New Jersey, and Delaware, have passed versions of the Lystedt Law.
Named for Zackery Lystedt, a middle-school football player who was permanently disabled after sustaining a concussion in 2006 and being put back in a game, the measure mandates that young athletes who exhibit concussion symptoms must immediately be sidelined and examined.
In college sports, where, according to Kutcher, reported concussions have jumped 30 percent since 2006, a few big-time football schools have created neurological adjuncts to their sports medicine units specifically to deal with the problem.
Kutcher, who heads the University of Michigan's, Michigan Neurosport, said his program needed to be emulated everywhere.
"The vast majority of [college] athletes who sustain a concussion," he said, "do not have access to concussion experts."
But perhaps the most telling evidence of how head injuries are transforming the culture of sports can be found in Canada, where tough, physical hockey has long been a source of national pride.
There, in the hockey-mad Toronto suburbs, parents concerned about the long-term health of their children formed a league where, even for players as old as 17, body checks are banned.
"With what we could see happening to our kids, combined with the growing body of medical research about the dangers of concussions, it was a no-brainer," said Bill Robertson, president of the Toronto Non-Contact Hockey League.
On consecutive second-quarter plays during the Eagles' loss to Dallas on Nov. 11, Vick was driven into Lincoln Financial Field's turf.
Even before the team's sideline medical personnel could gauge the extent of the dazed quarterback's injury, the Linc's concussion monitors had notified them that Vick would require a neurological evaluation.
According to NFL officials, nearly 200 similar calls have been made by these trainers in the sky since the monitoring began in 2011's postseason.
Among the incidents that precipitated the change came during a Chargers-Jets game last October, when San Diego's all-pro guard Kris Dielman staggered after what looked like a routine block.
Dielman became increasingly disoriented after the game, forgetting even how to shower himself. Then, on the long flight home, he suffered a grand mal seizure. At 31, his career was over.
It was later determined that San Diego had run the same play 15 times that Sunday. Dielman's seizure, experts determined, was the cumulative result of all those seemingly innocent collisions.
In much the same way, the concussion-driven changes in sports have arisen not from a single gruesome, highlight-reel hit but from the cumulative weight of bad news.
Once shrugged off as "bell-ringers," concussions began to be regarded more seriously early in this millennium. That's when the lawsuits from former players started to pile up and when the media turned its attention to athletes who had committed suicide or were suffering from dementia and/or depression, allegedly the result of long-ago head trauma.
Concussions, Kutcher and others point out, have always been prevalent in sports. And while a number of factors are to blame, the current epidemic, they argue, may be exacerbated by increased awareness.
Whatever the reason for the surge, there isn't a sport in America that is not now obsessed with the issue.
Football and hockey, with their high-speed impacts, seem both the most vulnerable and the quickest to respond. Though the NFL has drawn most of the concussion headlines, the NHL might have suffered more.
In Philadelphia alone, Flyers stars Eric Lindros, Keith Primeau, and Chris Pronger all had their careers ended or negatively impacted by concussions. And last season, one of the game's biggest stars, Pittsburgh's Sidney Crosby, missed considerable time with a head injury.
"The league worked diligently to increase the speed of the game," said Allen Walsh, agent for such stars as the New Jersey Devils' Patrik Elias and the San Jose Sharks' Martin Havlat. "And with increased speed necessarily comes increased collision."
The NHL, in response, replaced the hard glass atop its boards, mandated softer redesigned shoulder pads, and adopted Rule 48, which outlaws "contact with an opponent's head where the head is targeted and the principal point of contact."
"These are all things that we're doing to try and react and be proactive because it's something that's serious," said NHL commissioner Gary Bettman.
In baseball, a nasty 2012 collision involving Yadier Molina, the Cardinals' all-star catcher, may prove to be the concussion tipping point.
While MLB officials declined to be interviewed on the topic - a spokesman said discussions by the commissioner's On-Field Committee were "just at the concept stage" - rules that would prevent runners from steamrolling catchers, a practice as old as the game itself, are being considered.
The crisis also has changed many of the surfaces on which games are played.
A 2002 study by several Minnesota physicians confirmed what everyone already knew - that the rocklike artificial surface in the Vikings' domed stadium was "contributing to the high incidence of concussions."
Now, any newly installed NFL surface - whether artificial or grass - must meet specific Head Impact Criteria guidelines for resilience.
Those guidelines also are used in basketball, in which the risk of heads hitting hard floors has become a focus. Many schools and teams are installing new floors supported by layers of rubber or cushioned vinyl.
"There's certainly a higher concern now in almost all our markets," said Ron Cerny, president and CEO of Connor Sports Court, the nation's leading provider of athletic flooring. "Unfortunately, despite the resiliency of our wood sports floors, the top surface of wood is hard enough to still be a potential issue."
Much of the current concussion-related research concerns protective headgear. While baseball and hockey have used helmets for decades - and football even longer - soccer, the one major sport where the ball regularly comes in contact with the head, has resisted.
In 2010, a California researcher found that those who headed the ball most frequently did poorly in cognitive tests and complained more often of headaches and dizziness.
Soccer's helmet stigma has eased somewhat since Chelsea and Czech Republic goalkeeper Petr Cech has donned one in games after suffering a skull fracture in a collision during a 2006 English Premier League game.
Still, some critics suggest all sports headgear - even the air-cushioned football helmets now in use - are merely window-dressing.
"The only way to prevent concussions is not to step on the field in the first place," said Andrew Blecher, a sports medicine specialist in Southern California.
Perhaps nowhere are the concussion-wrought changes more controversial than in Canada, where the formation of noncontact hockey leagues has touched a national nerve
"There's definitely been a push-back," Robertson said. "At first the hockey establishment branded us an 'outlaw' league. Now they call us a 'rogue' league."
In the United States, USA Hockey mandated in 2011 that all its leagues for children under 13 are to be no-checking.
The success of the suburban Toronto league, founded four years ago by concerned parents, has given rise to similar noncontact organizations in Edmonton and Calgary and throughout Canada.
"We started with three teams, and now we're up to 13," Robertson said. "Everyone's seen stories about dementia and suicide. No parent wants a future like that for their kids. Someone needs to convince people like [outspoken hockey traditionalist] Don Cherry that this makes sense for kids. After all, 99.9 percent of these kids are never going to play in the NHL. Why risk their future health?
"Sports evolve. Football has changed. Why can't hockey?"
State of the Players' Lawsuit
In the midst of another football season clouded by the concussion issue, a federal judge in Philadelphia is weighing an NFL appeal to dismiss the class-action lawsuit joined by 3,300 former players.
That brief, filed in late August, was followed last month by a players' motion to dismiss it. In it, the plaintiffs contend the league was wrong in seeking to frame the issue as part of its collective bargaining agreement.
League attorneys contend the players were not deceived about the potential dangers of the head injuries that now are seen as a major health crisis in the sport.
The players, in the motion filed Oct. 30, claim the NFL permitted itself "to become the site of perhaps the gravest health crisis in the history of sports."
A decision on the NFL's motion is due to be rendered by mid-December.
While technically the case could go to trial soon afterward, attorneys have said the league would require at least six years to judge the viability of each player's case.
- Frank Fitzpatrick
Contact Frank Fitzpatrick at email@example.com, or follow on Twitter @philafitz. Read his blog, "Giving 'Em Fitz," at www.philly.com/fitz