Choose two evenly matched teams. Choose attacking end for each and assign positions as per a normal game. Inform players that they're playing under normal game conditions - with the exception of having 2 balls!
Give a ball to each (GK) who stands on the baseline. On 'go!' both teams work the ball in opposite directions and attempt to score.
Normal rules apply
There are 2 balls to watch out for, so players can either:-
Be an attacking passing option, or become a defender
Sometimes a team will have possession of both balls at once, so finding a free player is more challenging
Lots of voice is required to sort out the confusion
If a goal is scored, the team scored AGAINST get possession from the baseline
Relax the held ball rule to a certain extent, however apply a turnover to opposition if held for 5 seconds.
Intense effort will be required, so stop for a breather after 60-75 seconds.