As mentioned the contrast is way OTT and gives bad skintones.. quite red.. However having done a lot of boxing and looking at the exif I can see you where in simmilar conditions to what i am used to.. Do whetever you need to get the shot.. Personally I had the shutter down a bit from your 640 to 320 and still at iso 6400.. On a short lens you have more leeway with the shutter
To others asking.. Boxing is easy enough to get into at this level.. just contact your local boxing clubs they are always having exhibition matches with around 15 bouts...
Shoot from a nutural corner... have a stool/chair and dont bother if you ahve back problems because you will be doing a lot of twisting and moving taking a big strain on your back in funny positions..
I use a prime f2 35mm lens.. Quicker to find the shot when you take away the zoom and a 35mm on my crop camera is perfect for me.. gets my the full picture when they are at far side of ring and closups when they come near...
i have the center point on the canon ikle joypad thing so i can quickly move it about.. your at a shallow doff and fighters are seperated so I have the ability to quickly switch the point from one side tro the other.. set on 9 points.. set higher and it goes all over the place when your rushing ..
If shooting in a sports halll then you really should know how to manually set your white balance.. you dont want to be shooting in raw unless you have gig after gig of cards as you take so many shots.. no time for chimping.. If not a sports hall then see whichdirection lighting is coming from as its rarely evenly setup all round..
Some of mine.. includes younger aba at the blackburn venues
http://www.kipax.com/index.php?g=COMBAT
NOTE: Pics not meant as portfolio , not even meant to be the best.. they are for sale (counters all got reset last week)
As with any indoor sport.. never be afraid to push the iso up to max