Here I am, just spotted this. Hi Annaiso.
I haven't done much indoor sport pix but the problems I'd see would be lack of good light, colour temperature and fast movements of the combatant(s)
White balance can fix the second, the others are very dependent on your lens and lighting capability.
For actual 'fight' shots:
Centre spot focus, ISO 800 to get stop motion, continuous focussing, and multishot. You may find preset manual focus or prefocus and hold works but with wide open aperture and lots of opponent movement the depth of field may not be enough and you'll get soft shots.
Rear sync your flash for main lighting and will help colour balance. If you can add a few extra side lights to fill shadows and reduce harsh contrast the camera should cope with the rest reasonably well. I will use P mode ( not the green fully auto ) and preset ISO then let camera sort out f and speed for itself. Depending on your flash you may need to set speed to 1/160 if it isn't a KM unit with control. The 1/160 requirement for the flash will conflict with need for fast shutter for stop motion so you may get body ok but arm movement all fuzzed.
Lens ...... I'd have my 28-105 on, close enough not to require huge flash but I'd be staying back far enough to follow movement of combatants ( and to keep me outa trouble - same with rally cars LOL ). Zoom for framing.
Portrait is portrait, I ain't the expert there but posed shots in fight stances etc fit into that category.
Take lots of shots, and check results as you do, that's what LCD, Histogram, EXIF data are there for. If something ain't working change it till it does. Use the close up to chk blur, both movement and focussing because that's probably where your biggest problem will lie.
Hope this helps a bit, be interested to see a few pix later.