Boy spared detention for attack on rider

A 13-year-old boy convicted of hitting a man on the head with a bottle after the rider was deliberately knocked off his motorcycle with a rope has been spared more time in detention.

The boy, who can't be named, wasn't involved in tying the rope across the road, but did strike 19-year-old Lawson Mills outside the Perth train station on Wellington Street in December last year.

The child, who was 12 at the time and has already spent about three months behind bars, avoided more time in custody when he was sentenced in the Perth Children's Court on Wednesday for unlawful wounding.

He was granted a juvenile conditional release order for 10 months with an attendance and supervision component.