I watch the fights with my 6 month old son and 3 year old daughter. My boy just watches every now and then, then plays with his chew toy giraffe. My daughter watches a little bit, asks why they are fighting, tells the tv they should be nice to each other, then plays with her barbie.
I think if you explain that its a sport, your kid will get it.
I used to watch wrestling way back in the day with my grandfather, it was a cool bonding thing, and to this day I still pop up some of the old wrestling on youtube and think of my grandpa. All we had back then was wrestling to watch haha.