Even at amateur levels, attacking teams typically pour a few players into rucks to secure the ball. Smart defending teams recognise when this is a lost cause, opting to put defenders into the line to gain an advantage on the next phase rather than waste bodies in a ruck that is already lost. Even when the plan is to fan out and look to win the ball back on the next phase, it can be wise to leave behind a ‘nuisance defender’ to attempt a counter ruck – driving through attacking players who are not expecting a secondary shove. This player might be able to drive through and win the ball, or drive bodies back on top of the ball or scrum half and prevent them from using it quickly. Attackers leaning on rucks or otherwise passively positioned over the ball are especially vulnerable.
When a clear opportunity to steal the ball presents itself, someone can call to ‘flood it’. This calls the post defenders to join the ‘nuisance’ player in driving right over the ball to win possession. They must get low and drive up and through to clear bodies. Even if the ball is trapped, the referee will award the scrum feed to the team going forward when the play became dead.
The defending team needs to plan such tactics wisely, because if the attacking team manages to clear and play the ball, they may find themselves with a numbers advantage. Managing people at the ruck is a responsibility that typically falls to the scrum half.