While there is no way to know exactly why soccer appears to be getting more dangerous, parents and coaches share anecdotal reports of children being encouraged to play more aggressively and less-experienced referees who are hesitant to call fouls and eject players from the game.

Brian Hafter, of San Bruno, Calif., who has been coaching and refereeing girls’ youth soccer leagues for eight years, said he has noticed a substantial difference in the way kids play soccer now compared with how he and his sister grew up playing it.

“There’s no question that nowadays the players are much more physical, challenging for the ball, and as a result, can put themselves and their opponents in situations that can lead to more serious injuries,” he said.

Dr. Daryl Osbahr, who is the chief medical officer of the Orlando City Soccer Club and a consultant for U.S. Soccer, confirmed that the sport is causing more injuries.

“We have younger athletes playing sports over the course of the year at a higher level, and those factors will result in increased injuries,” he said. He also noted that overuse injuries are common now because more children are specializing in one sport.

Mr. Krause, whose son took the elbow to the head, said some youth soccer teams have reputations for being more aggressive and more likely to jostle and foul, but even after complaining to officials, there’s little that can be done to curb the behavior. “When you get to a certain level of soccer, you start to see that,” he said. “I know one kid ending up breaking his leg in the tournament. It’s horrible.”

Dr. Green, the pediatric orthopedist, said his own study of ACL injuries in New York State showed that in the past 20 years, there is a threefold increase in the rate of surgery for childhood sports injuries. One reason for the rise may be that soccer has become a more competitive sport and a path to college for talented athletes. As a result, more kids are playing on both school and club teams, as well as attending college soccer camps.