"I was touched and abused," the boy said after being asked what he meant by the word "molested".
The boy, then aged 14, said he, his brother and his friend showed up to a Saturday morning match early when McGrath called him into the changing rooms alone.
They sat down then McGrath started talking about why the boy had missed out on the Under 14s team and told him it was because the other players were more mature.
In the interview, the boy said McGrath told him to pull down his pants and masturbate.
"He said it would make me more mature physically and mentally."
The boy alleged McGrath then sexually violated him.
"I pulled up my pants and I tried to go. I tried to walk away. I was kind of too scared. I just slowly started walking away.
"He got his hand and he told me to come. He dragged me back."
The boy said McGrath told him: "I apologise if what I just did disturbed you or what we just did offended you", then started talking about the rugby match.
"I knew it was wrong but I had too much trust. I knew him since I was 10."
He said McGrath hugged him and told him: "Don't tell anyone about this. This can be our little secret."
The boy said he then found out the game had been cancelled so he, his brother and his friend went to leave but McGrath called him back to the club rooms. The club cannot be identified for legal reasons.
He gave him $10 and told him to buy the others a lollipop, the boy said.
On the way home, he told his brother what happened because McGrath had allegedly talked to them about how to clean their penises in the shower.
The boy said because their father didn't live with them, the coach said their mother had asked him to teach them.
On another occasion the boy said he'd injured his groin during a game and McGrath rubbed the area with soap.
Throughout the police interview, the boy spoke slowly, in short sentences and often took long pauses before answering questions.
Yesterday, McGrath's laywer, Siobhan Buckley, McGrath didn't accept any of the allegations and urged them to keep an open mind until the end of the trial.
The trial continues and is set down for two weeks.