Rules of Rugby
...."MOVING THE ....BALL
.... ....There is no blocking in rugby. Rugby ....does not have downs, and a team is not required to reach 10 yards ....and stop. Play is continuous like soccer. The person with the ball ....leads the attack. In rugby there are several ways to move the ball. ....Any player may carry, pass or kick the ball. Play is not stopped ....and continues when the ball hits the ground or when a player is ....tackled. The ball carrier must release the ball when tackled and ....roll out of the way so that other players on their feet can play ....the ball.
....Running: ....When running the ball, players may continue to run until they are ....tackled, step out of bounds or run beyond the goal line (see scoring ....a try). Players run the ball to advance toward the opponent's goal ....line.
....Passing: ....The ball may be passed to any other player. However, it may only ....be passed laterally or backward, never forward. Players pass the ....ball to an open teammate to keep it in play and further advance ....it.
....Kicking: ....Any player may kick the ball forward at any time. Once the ball ....is kicked, players of either team, regardless of whether or not ....the ball hits the ground, may gain possession. Players typically ....kick the ball to a teammate in an effort to advance it or to the ....opposing team to obtain relief from poor field position."
This explains the huddles, basically either side can gain position at any time.
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There is more at the link I posted.