If all the spaces on you side of the ruck are occupied and your scrum half is unable to get to the ruck to gather, you can choose to use the "Hand in" foul play.
One of your players involved in the ruck uses his hands to get the ball back to his team mates. To use 'Hands in' do the following...
1) During your turn nominate one of you players involved in the ruck to perform the foul.