Something worth keeping an eye out for.
Former All Black scrumhalf and now top Sky rugby commentator/analyst Justin Marshall believes there is a trend developing of Super Rugby players getting away with playing on in spite of being brought to ground in legitimate tackles.

Law 14. Tackle

Principle
A tackle can take place anywhere in the field of play. The actions of players involved in the tackle must ensure a fair contest and allow the ball to be available for play immediately.

Tackle
Requirements for a tackle
1. For a tackle to occur, the ball-carrier is held and brought to ground by one or more opponents.
2. Being brought to ground means that the ball-carrier is lying, sitting or has at least one knee on the ground or on another player who is on the ground.
3. Being held means that a tackler must continue holding the ball-carrier until the ball-carrier is on the ground.
Players in a tackle
4. Players in a tackle are:
1. Tackled player.
2. Tackler(s).
3. Others:
1. Player(s) who hold the ball-carrier during a tackle but do not go to ground.
2. Player(s) who arrive to contest possession in the tackle.
3. Player(s) who are already on the ground.
Player responsibilities
5. Tacklers must:
1. Immediately release the ball and the ball-carrier after both players go to ground.
2. Immediately move away from the tackled player and from the ball or get up.
3. Be on their feet before attempting to play the ball.
4. Allow the tackled player to release or play the ball.
5. Allow the tackled player to move away from the ball.
Sanction: Penalty.
6. Tacklers may play the ball from the direction of their own goal line provided they have complied with the above responsibilities and a ruck has not formed.
7. Tackled players must immediately:
      1. Make the ball available so that play can continue by releasing, passing or pushing the ball in any direction except    forward.  They may place the ball in any direction.
2. Move away from the ball or get up.
3 Ensure that they do not lie on, over or near the ball to prevent opposition players from gaining possession of it.
Sanction: Penalty.