It was commonly thought that Cowsill's involvement with the family band came to an abrupt end in 1969 when his father, Bud, caught him smoking marijuana, and he was immediately expelled by his father from the group. In fact, Cowsill's dismissal occurred one day after he and his father were in a drunken physical altercation in the lounge of the Flamingo Hotel in Las Vegas. The dispute was over Bud Cowsill's insults in relation Billy Cowsill's circle of friends, guitarist Waddy Wachtel in particular. State troopers had to be called to break up the fight between father and son. Billy Cowsill was dismissed from the group the next day. According to his brother Bob, Billy Cowsill's dismissal was the beginning of the end of the Cowsills as a group, since no other sibling could effectively assume their eldest brother's group leadership role.