The attack happened in Bramston Street between 4pm and 4.15pm on Tuesday.
The victim - a 14-year-old boy - suffered minor injuries and also had his rucksack stolen.
Two 13-year-old boys have been arrested in connection with the incident.
Officers understand there were a number of people in the area at the time and would like to hear from anyone who saw what happened.
Anyone who can help should 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.