The fight should take place on gymnastics mats or another soft floor (sand, grass, etc.)
Two players (or probably even more, but not too many) are standing on the fighting area. They bend towards the floor and hold their own ankles (or lower legs).
The objective of the fight is to move the other player(s) out of the playing/fighting field. Only pushing (with the chest or the shoulder) is allowed, but not using the hands, kicking with the feet or the head, etc. Of course, the fighters always need to hold their ankles or lower legs; if they let loose, they are out of the game as well. The (last) remaining player wins the round.