When two mates/pals join hands left to left right to right to show respect. They then proceed to kick or knee each others legs until one asks to stop or a bone is broken.
Sometimes done to resolve an argument but usually done for the crack.
Greg: Yo pal - you up for a kick-fight?
Cal: Yeah why not mate
During kick fight:
Greg: Ah stop I think you just broke my shin!!!
Cal: Haha you'll never mess with me again will you