Well, some of 'em are young white working class kids who like wearing nasty casual sports wear and horrible gold chains etc. They also have terrible music taste! So to a lot of people they would be "chavs", but they aint all bad.
Having said that, there's always a few idiots - which is why they stopped running the night bus to Knowle West a while back - and yes, I think you need to be vigilant if you are a stranger visiting Southmead coz they've got more than their share of problems for sure.