Justin Ryan, 18, and children in a neighbourhood off Torbay Road were playing with toy guns when a police officer drew his weapon. (CBC)

A St. John's father wants a full explanation of why a Royal Newfoundland Constabulary officer pulled a gun on his mentally delayed teenage son while he was playing with neighbourhood children.

The RNC said Tuesday, however, than an officer responded properly when the force received reports of a man carrying a gun in the Torbay Road area around suppertime on Monday.

Justin Ryan, who is 18 but has the capacity of a young child, was playing with younger friends in his east end neighbourhood. The children were using plastic guns that light up and make noises.

Things took a dramatic turn, though, when an RNC officer arrived and pointed a gun at Ryan. Witnesses said the officer ordered Ryan to the ground.

"It is kicking in, what could've actually happened," said his father, Mario Ryan, who believes the police seriously overreacted to the situation.

"I got knots in my stomach. And my wife is pretty upset."

Rodney Taylor, 15, said he told the RNC officer he was making a mistake.

Father Mario Ryan: 'It is kicking in what could've actually happened.' (CBC)

"He told us the way Justin reacted, that he didn't put the gun down right away, he was gonna shoot him, because they thought it was a real gun," Taylor told CBC News Monday evening.

"I was really scared.… People around here know what Justin is. They know that Justin has a mental disability. My biggest fear was probably that he was going to shoot Justin," Taylor said.

Speaking to reporters in St. John's on Tuesday afternoon, RNC Const. Paul Davis said that description of events is not accurate, and that Justin Ryan was the only person in the area when police arrive.

Davis said the toy looked like a machine gun from a distance, and that the officer responded according to standard operating procedures and according to his training.

He said two calls had been made to 911 concerning a man carrying a gun in the neighbourhood and the officer responded with the safety of himself, the teenager and the general public in mind.

Ryan told CBC News Monday night that another RNC officer arrived on the scene that evening. He said the officer described the incident as a serious misunderstanding.

Ryan said, though, that he wants a better explanation of why a police officer pointed a gun at his son's head.

The incident comes just three weeks after the RNC arrested an autistic teenager in Mount Pearl because officers mistook his condition for drunkenness. The force and the officers involved all have since apologized to Dane Spurrell, 18, who was held overnight in the downtown St. John's lockup and who was refused a call to his mother.