It happened at the North Plantation at around 21:00 on Wednesday.
Guernsey Police want to hear from any witnesses, particularly the passers by who were in the area at the time.
The victim was left lying on the ground after the assault, and was given medical treatment at the scene.
PC 97 Du Port is investing and can be called on 725111 or through Crimestoppers anonymously on 0800 555 111.
Pictured: The North Plantation.