It is tempting to say that this is a phase and will pass, but it obviously the cause of huge friction (*if* it is just a phase), plus I share your concerns about the friends he's made.
One thing you need to realise about modern secondary schools is that life is made hell for kids who 'the pack' deem in any way different. So answering teachers questions, not joining in disruption, are all good enough to get you a kicking at breaktime.
Some schools attempt to deal with this - many schools fiddle around the edges of it and find it easier to blame the victims or say it's down to bad individual teachers. It isn't . It's the start of gang culture. This is a very difficult time for a bright eager intelligent boy.
Judging from the time of your post, I'm guessing you had another confrontation this morning and you've snapped.
Conversely, the disruptive kids may have latched onto your son because they want to use him as leverage to get money out of his family. If he continues to hang around with them then sooner or later the requests / demands for money and fashion items will start.
I suggest you look for help and support inside and outside school. The person who is in charge of the year group pastorally is the first port of call. It might help to get a confidential meeting and air your feelings - don't even let your son know about this - and test the water. See how they react, what help they suggest. It might be as simple as kids being moved up or down a teaching set, or sideways into a different teaching group. It will be a long game even if the school is doing everything it can.
But beyond school you need to re-establish a way of you both talking together without it leading to a row, and some kind of family counselling might help - try asking for ways into this at your GPs, and if they don't come up with the goods, ask via your local youth services.
All kids become awkward at adolescence and they normally come back to their senses but it does take a couple of years - good luck, and try not to give up on him however hard it becomes.