My DD is 13 and we get a bit of attitude from time to time. One strategy I find very helpful is to make her stand there and repeat whatever it was she just said that was rude/stroppy/whatever in a way that is polite and respectful. That includes body language. If necessary she repeats it several times until she's got hold of herself. I also help model other ways to say what she wants to, or help her identify what it is she really means to say (often the rudeness is frustration about a related issue but not the thing they're having the huffy over). This works because it shows you're actually listening but also asserts your right to be respected at the same time.

I've also threatened to discontinue chocolate/coffee/sugary treats if grumpy behaviour doesn't improve. We also confiscate things out of her room (electronic gadgets work well here) and if the behaviour continues so do the confiscations. Perhaps try confiscating sporting equipment (it's one thing to be grounded, it's another to have to turn up at training without your gear, kwim?). And always check the simple things first - is he going to bed on time, or does he need more sleep? Is he really having problems elsewhere and the bravado is just a decoy (eg for the fact that he's struggling at school)?