Split players into two teams (no more than 5v5 - set up several mini-games if necessary). Pitch marked out with 2 goals. Size will depend upon your players' ability and numbers in the group but 20m by 10m is a good starting point.
This is an invasion game and the aim is to score a goal by rolling the ball through the oppositions goal.
Roll only to score. Cannot move with the ball, defending team must be a metre away from the player with the ball.
Practice getting down low with the head up (good fielding habits).
Change the sending action and combine skill so that players can still roll underarm but can also throw overarm to pass the ball (no overarm shooting).