Football has never been more popular. Some would say it has replaced baseball as America’s favorite pastime. But it’s tricky to predict what football will look like in another 50 years. Earlier this week, Jeff Miller, the NFL’s Vice President of Health and Safety, publicly acknowledged the connection between football-related head trauma and chronic traumatic encephalopathy (CTE). Miller’s acknowledgement is a big deal, as Steve Fainaru points out in a recent article for ESPN.com. It’s “the first time a senior league official has conceded football’s connection to devastating brain disease,” Fainaru explains.

The link between high-impact blows to the head and traumatic brain injury may seem obvious to us in 2016, but it hasn’t always been that way.The NFL’s formal admission before Congress goes against the findings of a league-funded 1994 research study, which repeatedly denied any links between football, concussions, and brain disease (“and attacked independent scientists who asserted otherwise,” according to Fainaru). More importantly, Miller’s statement could provide a leg up in the courtroom for the 5,000+ ex-NFL players who have sued the NFL for damages related to brain injuries. Cringe-worthy collisions are not worth the long term risks.

Conceptually, concussions aren’t so difficult to understand. Your brain sits inside your skull, surrounded by a thin layer of cerebrospinal fluid. But the fluid, which acts as a protective barrier, cannot provide sufficient protection if your head sustains an impact with enough force. During these “blows,” your brain bounces against your skull, damaging axons and the brain-blood barrier in their wake. Yikes.

Relative to other neurological conditions, scientists know surprisingly little about concussions. They understand how they happen, sure. But if concussions are point A and CTE is point B, scientists aren’t sure which route connects the two.

Many college and professional sports are aware of the danger that repeated concussions pose to pro athletes and are responding accordingly. The New York Times reported this week that the Ivy League now prohibits full-contact play during team football practices. And NFL and college football players aren’t the only ones at risk. The rise of competitive youth sports leagues means that athletes are experiencing those collisions at earlier ages, when the brain is still developing.

There’s a long history of athletes’ reluctance to adopt new equipment. In Major League Baseball’s early days, chest protectors and shin guards were derided as “tools of ignorance.” Since then, the MLB and also the NHL have made reducing players’ risk of injury a priority with required protective gear. The NFL needs to enact similar safety measures. Still, league officials must negotiate a tough question: when is safety a personal responsibility? At what point does inaction turn into negligence?

Both the MLB and the NFL have several helmet-related initiatives in the works. The NFL recently gave Vicis, a startup in Seattle, a grant of $500,000 to engineer a concussion-proof helmet; Vicis is slated to debut their new product this coming spring. The timeline below outlines the evolution of safety and equipment rules in major league sports.

PRO SPORTS PROTECTION THROUGH THE AGES

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1878: First baseball catcher’s mask is patented.

1907: New York Giants’ catcher and Hall of Famer Roger Bresnahan wears shin guards, becoming the  1st MLB catcher to wear protective gear in open view.

1939: John T. Riddell Company introduces a plastic football helmet, which proves to be more durable than leather models.

1940: Chicago Bears’ Dick Plasman becomes last NFL player to play in a game without a helmet.

1943: NFL mandates that all players wear helmets.

1955: Popularized by legendary Cleveland Browns quarterback Otto Graham, the “single bar” helmet is worn in the NFL.

1956: MLB “grandfathers in” helmets i.e. new players entering the league must wear helmets.

1962: The NFL requires that players wear helmets with face masks.

1968: NHL player Bill Masterton, a center for the Minnesota North Stars, hits his head on the ice in a game versus the Oakland Seals, causing a fatal brain aneurysm. Masterton becomes the first and only player in NHL history to die due to an on-ice incident.

1971: MLB requires all players to wear helmets while batting and running the bases. Catchers must wear them in the field.

1979: NHL makes helmets mandatory for new players entering the league; veterans have the choice of whether or not to wear one.

1983: All MLB players entering the league must wear a helmet with an ear flap.

1991: The first serious attempt by the UCI to introduce compulsory helmet use during the Tour de France. The UCI backs down after cyclists threaten to boycott the race.

1997: The last NHLer to play without a helmet, Craig MacTavish, retires.

2002: Riddell releases the Revolution (or Revo) Helmet, which most NFL players begin wearing.

2003: Turning point in cycling’s helmet policy due to the death of Kazakh Andrei Kivilev. The 2003 Giro d’Italia is the first major race affected. Bikers are still allowed to discard their helmets during final climbs that are at least 5 kilometers in length.

2009: Cubs pitcher Ryan Dempster becomes the first MLB player to wear Rawlings’ new S100 helmet, which offers better protection than the company’s standard helmets.