The incident occurred in Bramston Street, Brighouse between 4pm and 4.15pm on Tuesday, May 24.
The victim, a 14-year-old boy, suffered minor injuries and also had his rucksack stolen, police said.
Two 13-year-old boys have been arrested in connection with the incident, but officers understand there were a number of people in the area at the time and would like to hear from anyone who witnessed what occurred.
Anyone who can assist this investigation is asked to contact PC 3427 Lawrence at Calderdale District CID on 101, quoting crime reference 13220280762.
Information can also be reported anonymously to the independent charity Crimestoppers on 0800 555111 or online.