Rules and regulations
Rugby Union
Rugby union differs from football (soccer) in that the hands can be employed to move the ball. However, a player can only throw the ball backwards or laterally (i.e. not forward) to another player, but they may kick it forward.
This means that the majority of progress made by an attacking team occurs through a leap frog cycle of passing the ball, running to make ground, being tackled and repeating this process. Each of these cycles (greatly simplified) is called a phase of play.
Rules and regulations
Rugby Union
Rugby union includes the concept of "advantage". If one team commits an infraction of the Regulations, the referee will not stop play if the opposing team is in a position to gain a territorial or tactical advantage from the mistake.
Instead, he calls "advantage" and allows play to continue until he judges that adequate advantage has accrued, when he calls "advantage over", and play continues as if the original infraction had not occurred. If he deems that no advantage can accrue, the referee will stop play and award a scrum, free kick or penalty, as appropriate, at the site of the original infraction.
Rules and regulations
Rugby Union
The question of what is "advantage" and how long play should be allowed to continue to see if any advantage is gained, is a moot point: the referee is the sole judge of what constitutes "advantage" and different referees can and do take different approaches to this question.
But in general, if in subsequent "advantage" play a team has the chance to do what they could have done if the referee had stopped play for the infraction, then advantage has been gained and the referee will call "advantage over".
Rules and regulations
Rugby Union
So, for instance, suppose a team commits an infraction that would result in their opponents being awarded a scrum. If their opponents are able to take clean possession of the ball and advance it following the infraction, then they have done what they would have been able to do from a scrum — advantage is thus over.
If on the other hand their possession is "messy", or closely contested, then there is no advantage, and the referee will (or should) award the original scrum.
