They grabbed his phone and iPod and kicked him while he lay on the ground.
However, the men were spotted by a member of a nearby dojo.
Nathan Smith told his sensei and the rest of the students at Ninja Senshi Ryu and they rushed out to confront the thugs - all dressed in traditional black ninja garb.
On seeing the ninjas, the men fled, only to be later arrested by police.
"You should have seen their faces when they saw us in ninja gear coming towards them," the school's sensei, Kaylan Soto, told the Herald.
Link via Say Uncle | Photo via flickr user R'eyes, used under Creative Commons license