By Larry Fine

(Reuters) - The murder/suicide committed on Saturday by Kansas City Chiefs football player Jovan Belcher left the National Football League, its fans and health professionals struggling to understand what drove him to do it.

Belcher, 25, shot and killed his 22-year-old girlfriend Kasandra Perkins, the mother of his three-month-old daughter, in front of his own mother at home before driving to Arrowhead Stadium where he shot himself dead in the parking lot after thanking team officials for all they had done for him.

For the NFL, arguably the most popular U.S. professional sport, the tragic shootings cast the league in a frightfully brutal light as Belcher became the fourth player this year to die of a self-inflicted gunshot.

Former players Junior Seau in May, Ray Easterling in April and Michael Current in January all committed suicide.

A fifth suicide victim, former Chicago Bears player Dave Duerson killed himself by gunshot less than two years ago, leaving a note requesting that his brain be examined for a post-concussive disease that might have led to his severe depression.

An brain analysis showed that Duerson had a degenerative brain disease, as he had believed.

Details on Belcher's health have been slow to emerge.

Dr. Alan Hilfer, Director of Psychology at Maimonides Medical Center in New York, said just why Belcher suddenly snapped could remain a mystery.

"We may never know the reasons," Hilfer told Reuters in a telephone interview on Monday. "Something was terribly wrong."

The league has come under fire from former players who have joined to sue the NFL, claiming league officials looked the other way while the players were absorbing concussions that have led to long-term disabilities.

LOOKING FOR AN EDGE

Others suspect that the high-speed, muscular contact game leads players to look for a doping edge despite drug testing, and that can lead to psychological instability.

Chiefs Chairman Clark Hunt said Sunday that doctors and coaches told him they knew of no physical or emotional issues bothering Belcher, who reached the NFL as a free agent after going to the University of Maine.

"What do you look for? It's a very hard question to answer," Hilfer said. "Certainly you look for mood changes. Certainly you look for increased levels of impulsively and anger.

"These things sometimes occur so suddenly. Sometimes there is just no way you could possibly know that someone is going to perpetrate an act of violence of this magnitude."

Don Hooton, who founded the Taylor Hooton Foundation to promote steroids education in 2004, seven months after his son, Taylor, committed suicide following his use of anabolic steroids, suspects doping.

"Every time I hear a story like this, my mind runs immediately to anabolic steroids," Hooton said. "Not necessarily to the exclusion of anything else, but because anabolic steroids can affect the mind in these crazy ways.

"I hope when they do the autopsy on this young man, that they look for these substances because it's possible that what we saw was 'Roid Rage'" - a label given to the exhibition of anger among steroid users.

Hooton said that despite efforts in professional leagues to stem the use of performance-enhancing drugs (PED), recent studies showed that steroids use was on the rise among U.S. school children.

"It's not getting better - it's getting worse," said Hooton. "We better wake up, America."

LARGER SOCIETAL PROBLEMS

Dan Lebowitz, executive director of Sport in Society at Northeastern University, said he saw the Belcher tragedy as something that speaks to societal problems transcending sports.

"This is an issue of men's violence against women, not just football players being too violent," Lebowitz said. Continued...