Pritchard confirmed the teen had crashed through the window, sending glass spraying across the forecourt and tables fronting the carpark off Thackeray St.
Several customers were in the restaurant when the fight broke out, and CCTV images are available to police who, Pritchard said, believed the incident involved mainly just the two men who were injured.
Police were yet to interview the pair. One was "known" to police, the other not, he said.
Pritchard said at least two witnesses were believed to have intervened to stop the late-night fight.
The dine-in area and main counter of the restaurant was closed but the drive-through was busy.
The restaurant is staffed mainly by young people. Some of their family members expressed concern on a Facebook thread, which included parents worried about the traumatic effect on teenagers and children who witnessed the violence.
One commented her daughter was so traumatised she didn't want to go back to the restaurant.
"Poor girl," another responded.
"She has to live with that. Nobody deserves to see that crap."