On a turf field at a Washington, D.C., elementary school not long ago, the Jaguars were playing the Thunderbolts in a big fifth-grade boys’ soccer game. The airborne ball struck a Jaguar head. It bounced to a Thunderbolt head. Then another Thunderbolt head. And then a Jaguar head and another Jaguar head and finally to the ground. With each successive header, the parents oohed and cheered—how cute! how cool!—their delight echoing off of the school’s brick walls.

The game was part of a daylong school soccer tournament, and I was watching with the all-girls rec team that I coach. I don’t allow my team to head the ball. Naturally, then, when the girls saw the Jags and T-bolts Ping-Ponging the ball around the field with their noggins, they turned to gauge my response. I smirked and shook my head. Then, with the timing of a seasoned stand-up comic, one of the girls announced, “No wonder they’re all so dumb!”

It was less a statement of fact, of course, than an exquisite preadolescent takedown of the opposite sex. But lurking, literally, beneath every header is a mystery: Can the routine act of heading a soccer ball cause traumatic brain injury? The answer to this question still isn’t entirely clear, but I believe we know enough to say this much: It makes no sense to allow young children to knock their heads repeatedly against a soccer ball.

This week, the New York Times reported some sobering and potentially troubling news for the sport: the first documented case of the degenerative brain disease chronic traumatic encephalopathy, or CTE. The victim was Patrick Grange, a 29-year-old former college and semipro player who died in 2012 of amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease. “We can’t say for certain that heading the ball caused his condition in this case,” Boston University neuropathologist Ann McKee, who examined Grange’s brain, told reporter John Branch. “But it is noteworthy that he was a frequent header of the ball, and he did develop this disease. I’m not sure we can take it any further than that.”

McKee has found CTE—which can lead to memory loss, depression, dementia, and other diseases, including ALS, with which Grange was diagnosed at 27—in the brains of dozens of athletes. She said the sort of frontal-lobe damage in Grange’s brain had been seen in other deceased athletes in their 20s, but that all of them had played football. She also noted that the damage corresponded to the part of the head typically used to strike the ball—the upper part of the forehead. Grange, his parents told the Times, started heading a ball when he was 3 years old.

As a teenager in the 1970s, I watched Pele, when he played for the star-studded New York Cosmos, explain how to head a ball. First he pointed to his forehead. Then he placed the thumb and forefinger of each hand in front of each eye and opened them both wide. Then he dragged his thumb and index finger across his closed mouth. Moving his head and shoulders back in tandem to prepare to strike the ball, Pele demonstrated how the neck muscles needed to be tensed at the moment of impact.

Failure to take Pele’s steps can result not only in a misdirected ball but in greater force imparted to the brain. That’s because a header is a collision that can cause the brain to shake inside the skull. “If you take a header off the back of your head or the side of your head and it whips your head around, there are much greater forces, 40 or 50 G’s, as opposed to a proper header where the G-force is under 20,” Dr. Robert Cantu, a colleague of McKee’s and the co-author, with Mark Hyman, of the 2012 book Concussions and Our Kids, told me recently.

Most prepubescent children aren’t capable of making the necessary preparations to head the ball; they’re just not strong enough or aware enough or coordinated enough. And if they do keep their eyes open and their mouths shut and strike the ball with their foreheads, their neck muscles, even if tensed, aren’t strong enough to prevent their heads from absorbing what often are elevated G-forces. Plus, Cantu says, the heads of children are bigger and wobblier in proportion to the rest of their bodies than those of adults. The wobblier the head, the more likely the brain will shake inside the skull upon impact. Just as 6-year-olds aren’t developmentally ready to pass the ball to a teammate, 10-year-olds aren’t ready to head the ball.

(And girls might be less ready than boys. Girls’ heads are typically smaller than those of boys, and their neck muscles tend to be weaker. A similar blow to the head, consequently, might concuss a girl but not a boy. In a 2005 study at Temple University, the head and neck of female subjects exhibited “significantly greater” angular acceleration and displacement in response to an external force compared to that of the male subjects. Translation: The female heads and necks moved more and faster, increasing the risk of brain trauma.)

It shouldn’t take much to persuade an impartial observer that heading in youth soccer is pointless. Watch a recreational or even an elite travel soccer game involving preadolescents. Heading, when it occurs, is usually a random act. Eyes shut. Head scrunched into neck. Shoulders clenched. The ball usually makes contact on the top or the rear of the skull. It isn’t directed to a specific place—to a teammate, toward the goal, out of bounds. It ricochets to points unknown, in direct opposition to a fundamental teaching tenet of the sport. Players would get better at soccer by learning to control the ball out of the air with other parts of their bodies.

Cantu endorses a ban on heading for kids under 14. That’s because of the dangers of heading itself, but also what else can happen during the act: the head colliding with other heads, elbows, and the ground. A 2007 study by researchers at Ohio State University and Nationwide Children’s Hospital in Columbus, Ohio, found that high school soccer players, both male and female, sustained the majority of concussions via contact with another person. And there’s no disputing that concussions are a serious risk in the sport. Football showed the highest incidence of concussions among high school athletes in the Ohio State study, 47 for every 100,000 games and practices. But girls’ soccer was second with 36 per 100,000 and boys’ soccer third with 22 per 100,000. Former Major League Soccer players Taylor Twellman, Alecko Eskandarian, Josh Gros, Bryan Namoff, and Ross Paule retired following repeated concussions. Two standout women’s college players quit the sport last fall because of concussions. U.S. national team star Abby Wambach, who is known for her heading prowess, was concussed last year when she was struck by a ball during a game.

But the mere act of head meeting ball is getting attention, and not just at the youth level. In a study published last year in the journal Radiology, researchers at Albert Einstein College of Medicine in New York used advanced magnetic resonance imaging on the brains of 37 amateur adult players who had played an average of 10 months over the previous year and 22 years overall. The players who headed the ball above a threshold of 885 to 1,550 times a year exhibited signs of nerve damage associated with traumatic brain injury. Those who headed the ball more than 1,800 times a year showed signs of compromised memory. “Repetitive heading could set off a cascade of responses that leads to degeneration of brain cells over time,” said Dr. Michael Lipton, who headed the study.

In another study last year, this one by researchers at the University of Texas Health Science Center at Houston, girls on a high school soccer team were given an iPad-based reaction test immediately after practice. Players who had headed the ball, doing so between two and 20 times, recorded slightly slower response times on the test. “These findings demonstrate significant and specific cognitive changes in female high school soccer players who head the soccer ball during practice,” the study concluded. Another 2013 study, by scientists at Imperial College London, found that the force of an average header was like a punch from an amateur boxer.

If these sorts of studies appear to be an outgrowth of the National Football League’s ongoing concussion crisis and the attention it has engendered, they’re not. Evidence of a connection between repeated soccer heading and brain trauma, and interest in it among brain scientists, has been around for decades. In June 1927, the New York Times reported that a player on Palestine’s soccer team, in town for a game against the New York Giants of the American Soccer League, “has been suffering from a slight concussion of the brain” that the team’s trainer said “was caused by the frequent heading of the heavy, rain-soaked ball.” A 1972 study in the British Medical Journal was titled “Footballer’s Migraine.”

A 1989 study found “significantly increased incidence of EEG disturbances” in the brain scans in 69 professional players in Norway. A 1998 study of 53 active professional players in the Netherlands found that “performance on memory, planning, and visuoperceptual tasks [was] inversely related to the number of concussions incurred in soccer and the frequency of ‘heading’ the ball.” A 1999 study of 33 amateur Dutch soccer players found impaired performance in memory and planning. In 2002, a coroner ruled that former English professional player Jeff Astle died at 59 from dementia caused by repeated headers. A 2003 study of 60 soccer players in Florida aged 18 to 29 found that those who headed the ball the most showed impairment on neuropsychological testing. A 2007 study of 10 college soccer players observed “decreased gray-matter density and volume” in parts of the brain.

Like McKee discussing Patrick Grange’s death, the scientists involved in many of those studies have cautioned against reaching broad conclusions about the long-term effects of heading, and other studies have found little or no correlation between heading and brain trauma. Given the prevailing belief that heading is an indispensable part of soccer, the lack of a clear scientific consensus has meant that youth leagues have taken little action. More than a decade ago, after a flurry of publicity about heading and brain injury, the American Youth Soccer Organization voted down a proposed rule that would have banned heading for players under age 10. Today the organization, which represents more than 500,000 youth players nationwide, toes a cautious line. “AYSO does not recommend heading below the age of 10,” the organization states. “Coaches are not encouraged to teach or practice heading at these early ages.”

My daughter’s soccer league in Washington has a similar policy, but coaches and parents aren’t told about it and would be hard-pressed to find it online. In any case, many coaches teach heading because they believe it’s a critical soccer skill, and kids head the ball because it looks like fun, and because parents don’t know any better. A national soccer program got a lot of attention when it banned heading—but it serves only children ages 3 through 8, who rarely get the ball into the air anyway. I haven’t found an example of a league for older children that has banned heading. (If you know of one, please drop me a line.)

Dutch neuropsychologist Erik Matser, who has conducted several studies on soccer and heading, told the Times that players under 17 shouldn’t head at all during training. “Let’s first do more research before you say heading is safe for kids,” he said. “We’re walking on a razor’s edge. There is some concern with professional players, and it could be dangerous.” But Matser didn’t say that in this week’s story about Patrick Grange. He said it in 2001.