if you were doing 15 stock per crew it'd be
player 1-a vs player 1-b starts with 5 stocks. They just fight a regular match.
Player 1-a wins with 4 stocks, cause player 1-b sucks.
Player 2-b comes in next round.
Before they start, player 1-a suicides once, so he's back to his 4 stocks.
Somebody has to give an audible go signal, then player 1-a and player 2-b starts.
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You generally do crews on retardedly neutal stages (i dont know what they would be in brawl, since the only really neutral stage is smashville). Everybody must select their character before the crew battle starts, and you generally write it on a paper along with your starting member (so you cant **** the other crew).
If you allow counter picking, then the player who is in is allowed to change characters.