Leo Anderson was in the middle of a baseball game when he threw a ball he had just caught, heard a crunch in his elbow and fell to the ground.

That sound was a growth plate in his elbow breaking, and it ended the now-15-year-old’s season last spring.

Doctors said the break was caused by overuse, and the Highland Park, Ill., teenager had surgery to place a pin in his elbow to stabilize it.

Anderson, a catcher who had been trying out pitching, wore a cast for 12 weeks before his comeback this fall, playing for the Slammers club team in Lake County. The high school freshman also had physical therapy until November and said he hopes to play for his high school team in the spring season, in addition to his other team.

But his father, Bill Anderson, said he now closely monitors his son’s play, and that the injury was a warning. Leo, like many youth athletes, plays baseball 10 months out of the year.

“Quite honestly, it just didn’t occur to me that he was overusing his arm,” he said.

Doctors say overuse injuries in youth sports have increased significantly in the past decade. They blame it on children focusing on one sport early on and playing it year-round, sometimes on multiple teams at once.

“Sports specialization has led to almost an epidemic in sports injuries,” said Dr. Elizabeth Matzkin, surgical director of women’s musculoskeletal health at Brigham and Women’s Hospital in Boston and assistant professor of orthopedic surgery at Harvard Medical School. “Kids are fatigued, and they’re not strengthening the way they should be.”

Matzkin said that, in the past decade, she’s seen overuse injuries in young athletes that she used to see mainly in adults.

“Over the past 10 years, you’d maybe see the occasional high school ACL tear. Now you’re seeing it in 12-, 13-year-olds,” she said. With such injuries at 13, “are you going to have arthritis when you’re 30?”

While doctors and physical therapists say they can treat the injuries, some worry what will happen as these young athletes grow up — when old injuries could turn into chronic problems.

“We can get you back playing your sport, but what we can’t do is prevent your arthritis in your knee,” Matzkin said. Then “you’re seeing young women in their 30s who can’t keep up with their kids in the backyard.”

Doctors say it’s largely up to parents and coaches to try to prevent these injuries through cross-training and rest. But that message can be hard to follow in the increasingly competitive field of youth sports, in which more parents seem to have their sights set on college scholarships and even professional play for their kids, said Dr. Andrea Kramer, a pediatric orthopedic surgeon at the Illinois Bone and Joint Institute.

Kramer, who treated Leo Anderson, said she has also seen more overuse injuries in recent years, and at younger ages.

“I’m seeing kids from 7 on up for overuse injuries,” she said.

The injuries come in the forms of sprains, breaks, stress fractures and other problems that cause “much more increased pain at a much younger age” than she used to see, and span many sports.

Kramer said children are at risk for these injuries because they are still growing and growth plates are shifting. She said she advises these young athletes and their parents to try more variety in sports or cross-conditioning, and stresses the importance of rest. Societal pressures seem to play into the desire for high achievement in sports, often leading to overplay, Kramer said.

“If we could convince people to not specialize in one sport at a young age, it would help a lot,” she said.