A teenage boy needed surgery to stabilise a broken ankle after he was assaulted by another youth in St Leonards.
Police said it happened at the junction of the A2102 London Road with Springfield Road at about 4.20pm on Wednesday, October 23.
A 15-year-old boy suffered a broken ankle which later required surgery.
Police now want to speak to anyone who saw what happened.
In particular, officers would like to speak to the driver of a white van believed to have stopped in Springfield Road while waiting to turn left onto London Road.
Anyone who witnessed the incident or who may have dash-cam footage that captured it is asked to contact Sussex Police online or by phoning 101, quoting serial 879 of 23/10.