Agree with everything Pancake Man said. There is not enough light in the gym, so to compensate the camera (or its operator) is lowering the shutter speed (creating motion blur), and/or raising the ISO light sensitivity (making it grainy).
He could try a monopod, which helps avoid camera-shake blur, but that won't help subject motion blur. At very least, the monopod will be useful shooting other (outside) sports in the daytime. Just remember to turn off the IS image stabilization on the lens, or put it in "panning" mode if the lens has it, or else the IS will fight the monopod and make things worse.
He can shoot a wider aperature (lower f/number like f/2.8 or f/3.5) to let more light in, but if you open your 50mm all the way up to f/1.8, the depth of field in focus will be paper thin and unforgiving, so you will find it hard to shoot moving subjects (wrestlers) in-focus.
It would help to get RIGHT UP CLOSE, rather than sitting back at a comfortable distance using the zoom/telephoto. That eliminates some of the blur the old-fashioned way.
You just need more light, when you get right down to it. Is flash allowed in the gym? That would make a WORLD of difference. You don't have to (or really want to) aim the flash right at the wrestlers. Plug a speedlight flash into the hotshoe, and aim it at the ceiling, so it bounces back down softly on the scene. It won't be in anyone's eyes, and it will also prevent ugly direct-flash shadows. With the added light, you can shoot the fast shutter to freeze the action without having to up the ISO above 400 or so, which will prevent the grainy-ness.