It is the first part of the Real Betis Balompié's anthem, that was composed by José Alonso Fernández (music and lyrics) in 1982.
Lyrics
We're all here to sing you song, We're crowded like cannonballs, And there's nobody that can deal with, These fans, That even if we're last we always see you as the champ, Betis, Betis, Betis...