I doubt that any of the teens were 13-year-olds. A couple of husky 17 - 19 year olds could cause harm - and we don't know if the man is tall, fit, fast...
Hindsight is of course 30/20, but the thought of a gang of punkass teenagers ganging up on some guy just isn't - wasn't - something that would be reasonably anticipated. 
I'll give you a star for old time's sake....

"YOU ARE WICKED!" Sweet-talkin' me now, DG??