A hardcore crew is a group of kids who know each other from punk/hardcore/metal shows.
These kids usually have plenty in common: they're middle class white kids, looking for the backing of their friends during fights, and when they're in other troubling situations.
Almost every hardcore band, and even bands that aren't hardcore but grew up around a scene have a crew affiliation. Some crews hate other crews, while some small crews group together.
Hardcore kids with Myspace sometimes put their crew name or acronyms in fromt of their myspace name.
I went to a show last night and there was this hardcore crew called "No Push Mosh Crew" that stopped me from push moshing.
The hardcore crew F.S.U. has heavy ties to almost every alternative music band out of Boston, they're also largely apart of the "Boston Beatdown" video series.
Myspace example name: FYWE (Johnathon) XXX