Dealing with a dirty/mauling fighter.

Hey guys! New poster here. I am looking for some advice, can anyone offer any pointers on:

-How to Box against an opponent who wants to clinch, excessively, &wrestle you to the ropes, push you down, etc. If the referee isn't offering any kind of relief, as a fighter, what can you do to combat this type of opponent? I attend many small shows and commonly see better boxers being drug into a sloppy, ugly match, by a less polished, mauling kind of fighter, who only seems to want to wrestle, and score single blows in the clinch, rabbit punch, lean on &push his opponent to the canvas. My brother is a young boxer and has encountered this several times, &it has troubled him. I'm trying to find some sound advice on this to offer.
Thank you all for your time!
Regards

Learning to move properly is a good place to start. A lot of young boxers move before they need to, and more than they need to, and they move in straight lines. This takes you into the ropes and corners. You don't move in straight lines and you don't move 'side-to-side' ("lateral movement") You move in circles and step around an opponent.
The current common 'defense' that consists of putting your hands in front of your face guarantees that your opponent will do as he pleases because you can't see him and you can't punch from there. You aren't even in good position to grab him properly to turn him and get out of the clinch.

Excellent, thank you. After reviewing footage of one of his most recent bouts, I see that often when his opponent dove in to grab him, he would back straight up, his opponent was able to grab him each time and drag him into a foul filled clinching match.

Thanks again for your insight!