You mean Vamos Boca? I think Boca refers to Boca Juniors, a football club in Argentina. (They speak Spanish there.) "Vamos Boca!" is something like "Go Boca!" and it's sort of a chant, just like how e.g. fans in England chant. (Go Reds! Go Liverpool! Go Chelsea!) In French they use a similar chant: "Allez les bleus!"