BOSTON (AP) -- A young boy who dreamed of a professional hockey career gradually lost interest in the sport and turned to drugs and alcohol after he was sexually assaulted by his coach, a prosecutor said Tuesday.

The teenager "showed great promise," but became troubled after years of hiding the alleged abuse, Assistant District Attorney David Deacon said Tuesday during opening statements in the sexual assault trial of Robert Richardson.

Richardson, 51, has pleaded innocent to charges that he sexually assaulted and abused the boy on three different occasions in 1998 and 1999.

Prosecutors say the first incident happened on July 30, 1998, when the boy was 14. Richardson allegedly assaulted the boy in a dorm room during an International Hockey Academy camp held at Boston University. Richardson, an NHL scout, was the director of the camp.

Richardson's attorney, Robert George, suggested during his opening remarks that the boy lacks credibility and is lying about the abuse for financial gain. He questioned why the teen didn't go to police immediately, waiting more than three years after the last alleged attack to first report it. And he said the teen switched his story when interviewed by investigators.

According to prosecutors, the boy loved hockey and tried hard to excel in the sport by taking on extra practice and going to prep schools that had reputable ice hockey programs.

But when the teen entered high school, he got involved in drugs and alcohol, started failing his classes and eventually quit playing hockey. Prosecutors attributed his behavior to a troubled teen hiding a horrible secret.

George said the teen was angry he wasn't excelling as much as he wanted to in hockey and took it out on the coach, who is well known for helping several young hockey players advance in their careers.

The boy, George said, "stands alone here in making these allegations."

He "didn't crash until after he was cut from (his prep school's) hockey team," George said.

The trial was expected to continue Wednesday, and last up to eight days.