Some Great Basics Info from the All Blacks Rugby:
A More In-Depth Look at Rugby from USA Rugby (pdf):
Here’s a Look at One Particular Rule…
To stop a player running with the ball, the opposition will try to tackle them. Only players carrying the ball can be tackled. The tackle is complete when the ball-carrier is brought to the ground; this is judged to be the case as soon as a knee touches the ground while being held by the opposition. The tackler is designated as any player that also goes to ground when making the tackle. If no player goes to ground when tackling a player, then there is no tackler. The tackler has to immediately let the tackled player go and get to their feet before attempting to compete for the ball. If they do not get to their feet, they must roll away from the tackled player. The player that is tackled must immediately play the ball by pushing, passing or placing it in any direction. If a player is involved in the tackle, but does not go to ground, they must also release the tackled player, allowing them the chance to play the ball. Only players on their feet, and supporting their own weight, may pick up the ball and any players on the ground must not prevent them from gaining possession. Except for the tackler (player who went to ground when making the tackle) and the tackled player, all other players must enter the tackle area from behind the ball. The tackle must not be dangerous. Dangerous tackles are ones that make contact with their opponent around their neck or head, with a locked elbow and extended arm (“stiff arm”), without using their arms (“shoulder charge”), when they are in the air, when they don’t have the ball, or ones that drive or drop a players head or neck into the ground while their feet are in the air (“spear tackle”). Using a foot to trip a player is also illegal.