New reports of brain damage to soccer and rugby players are leading to a re-think of how jiggling the brain during a game could lead to the kind of long-term damage long associated with slam-bang sports like football and boxing. But medical researchers aren’t yet ready to call for the end of contact sports.

Some athletes get hit hard many times and don’t develop conditions such as chronic traumatic encephelopathy (CTE), the disease diagnosed in Major League Soccer player Patrick Grange, who died in 2012 and a former pro Australian rugby player, Barry Taylor, who died in 2013. Those who do could have some kind of genetic susceptibility to developing these injuries or a pre-disposition that isn’t yet well understood.

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Patients with CTE have an abnormal build-up of protein that can block or disable neural pathways controlling things like memory, judgment and fear. CTE can be diagnosed only after death and has been linked to psychological problems such as depression, anxiety and substance abuse.

But researchers still don’t know whether athletes should be worried about big hits that cause concussions, or smaller “pre-concussive” collisions that occur as a routine part of the game.

“This area is a rush to judgment over what we know or don’t know,” said Thomas McAllister, chairman of the department of psychiatry at Indiana University and a leading expert in traumatic brain injuries. “Because there is a lot we don’t know.”

McAllister explained that scientists have known about the dangers of getting hit on the head since the 1920s when they diagnosed a form of dementia in boxers. They called it neurologica pugilistica. In recent years, the same condition has become known as CTE.

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Last year, McAllister and his colleagues completed a study of NCAA football players over the course of a season, as compared to a similar group of track and field athletes. They tested both groups for cognition and memory, as well as performed sophisticated diffusion tensor imaging of their brains. While they all performed equally on the tests, they found about one in five football players experienced changes to a part of their brain called the corpus collossum, which lies in the middle of the two hemispheres.

McAllister said the degree of change was related to how hard and how much they were hit during the season, something measured with small accelerometers implanted into the helmets.

“All we can say with our data is something changed over the course of season,” McAllister said. “We don’t know if we studied them five or ten years later, if they would be doing alright. It’s possible (the changes) may heal or reverse themselves during the off season, but we don’t know.”

Real Madrid's superstar English player David Beckham heads the ball during a game at Sport city in Madrid, Spain, in 2003.Getty

Researchers at Boston University have been examining the brains of pro football players for the past several years. The players' brains were donated by their families after the men experienced early dementia as well as psychological problems. The CTE Center found 45 of the 46 NFL players they examined had CTE.

“The brain doesn’t know what causes repetitive trauma, whether it's soccer or baseball or other sports,” said Robert Cantu, professor of neurosurgery at Boston University School of Medicine, and an investigator in the BU CTE Center. “The brain is susceptible to CTE and you may wind up with it.”

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The list of sports with athletes and CTE has expanded to include hockey stars, NASCAR drivers and baseball players. This year, MLB instituted a new rule to help avoid collisions between base runners and catchers at home plate.

While that rule change is relatively minor, one sports medicine physician says that medical researchers will have to come up with better data about CTE and head injuries before some sports make wholesale changes in equipment or rules.

“Are you going to ban heading?,” asked Rocco Monto, consulting physician to USA Soccer, the sports organizing body, and a Massachusetts physician. “How are you going to do that without data? Soccer players and fans are about as traditional as you are going to find. If you look at the structure of soccer and look at 100 years ago, it doesn’t look a lot different than today.”

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Monto noted that bigger pads and helmets haven’t stopped injuries in football. He said that one of the challenges for both researchers and doctors is that CTE may be the result of cumulative hits to the head.

“That makes it all the more difficult when diagnosing a patient," Monto said. "Is it a clinical depression episode or related to head injuries? That’s the challenge for clinicians.”

Cantu and McAllister respond that new research currently underway may take some of the doubts away from the CTE equation, identify at-risk athletes through a genetic test, and perhaps even find a way to diagnose early stages of CTE in athletes before they leave their playing days behind.