Crew battle are usually like you have crew vs crew, and each member of each crew has four stock.
Sometimes each player picks the character they will play beforehand, and has to stick with that character throughout the battle, but also sometimes character counterpicks are allowed.
but say theres ten people in each crew.
the captain sends their first player in...i think the first player is selected in a double blind sort of way...and after the first match, the winner enters the second match with however many stock he has left over (i.e he sd's as many times as needed in the next match)...and the losing team captain selects who they want to send in next.
this continues until all players on one team have been eliminated.