When I see professional sports, sometimes I see traces and signs of ancient tribal wars in those. When two teams contest, it is like two tribal groups fighting; may be for food or for some treasure. Goal post is where food/treasure is. Two halves of the playground are their respective tribal villages - they try to storm into the opponent's which try to 'defend' what they got. Bats, sticks, and other sports accessories are like war weapons. In case of individual sports like boxing - it is like two tribal chiefs fighting to settle the matter between them while others watch them fight. The Trophy or the 'Cup' represents the treasure for which they fight.
Some sports like archery, sword fighting, have remained near exactly what they were meant to be, as have boxing and wrestling - these are actual fights; we have just given away the slay-the-loser part!
Professional sport brings out same kind of savage passion in the viewers - and as much physical and savage the sport is - so much more passion it generates; so we find two teams' supporters fighting each other even in the stands!
Teams' uniforms are meant to distinguish one tribal race from the other. Cheerleaders represent the women of the fighting tribes - who can't fight as they have to protect babies, so they cheer up the male fighters who fight also to protect the women.
To make it more apparent to the naive they also name the teams on those lines - Knights, Riders, Chargers, Tuskers, Warriors; in IPL; Gladiators, Predators, Force, Sharks, Storm, etc in AFL.
It is no coincidence that military-men do great in sports as compared to civilians, because of overlap in skills needed... :)
Professional competitive sports can be seen as just a civilized manner to keep the passions of the uncivilized tribal wars alive somewhere in our genes. Don't slay me for this now; even for sport :)