In the Roman form of chariot racing, teams represented different groups of financial backers and sometimes competed for the services of particularly skilled drivers. These teams became the focus of intense support among spectators, and occasional disturbances broke out between followers of different factions.
For the same reason anyone enters a race, to show who is the fastest, nastiest, most violent driver around. They couldn't put sponsors stickers on their horses, so they used the chariot, eat at Ceasers pizza, Cleopatra's house of Togas. The chariot was their tank, so you take on other tanks to see who's the toughest
"Well, she got her daddy's car and she cruised through the hamburger stand, now Seems she forgot all about the library like she told her old man, now And with the radio blastin' goes cruisin' just as fast as she can, now
And she'll have fun, fun, fun 'til her daddy takes the T-bird away fun, fun, fun, 'til her daddy takes the T-bird away
Well, the girls can't stand her 'cause she walks, looks, and drives like an ace, now She makes the Indy 500 look like ROMAN CHARIOT RACE, now A lot of guys try to catch her but she leads 'em on a wild goose chase, now
And she'll have fun, fun, fun 'til her daddy takes the T-bird away fun, fun, fun, 'til her daddy takes the T-bird away ..."