Would the Nikon D5100 be good for shooting still photos of MMA or Boxing?

Just looking to get into photography. Not looking to spend a lot of money but a good amount for a entry level dslr. I want to be able to catch good photos of MMA, Boxing, etc sports.

The biggest problems "prosumer" digitals have in shooting sports are a: the cheap kit lens, which has a tiny max aperture usually around f/4, and b: slow autofocus.

However, with MMA and boxing, you needn't use autofocus at all. With a little practice you can get good results in manual focus. The D5100 has one of the best sensors available right now, and it is compatible with affordable lenses like the AF-S 50 1.8, around $200, that will give you fantastic image quality with minimal cost. If you're ringside, a wide lens is better. If you're up in the crowd, you'll want to get something more on the tele side.

If you want to zoom and get comparable image quality, you will have to spend $500+ on a lens, like the AF-S 17-35 2.8, for about $1500, and there's nothing wrong with putting an expensive lens on a cheap body. The body will last you a few years of steady use. The lens will be with you forever.

You'll need a body with a focus motor like the D7000 if you want fast accurate AF for sports.

You may also want to upgrade your focusing screen if you plan on using manual focus.

James gave you really good advice.

Venues that host professional sports usually want to see your press credentials when you bring in a camera like that.