Bassnectar concert.. something weird happened?

i was at a bassnectar concert where obviously lots of ppl on drugs are at and some sketchyy **** happens. i was walkin through the crowd tryin to get back to my third row spot and someone like stabbed my with something really sharp im pretty sure a knife??? and slit my shirt and then just pulled it out.. like it didnt stab me. but they ripped a small rectangle on the back of my shirt out!!! why would they do that??