The IRB website says this in 'Section 10.4 - Dangerous Play and Misconduct':
It doesn't make it very clear if that deserves red or just a yellow but it does make it clear that dropping the player is still dangerous play.
(j) Lifting a player from the ground and dropping or driving that player into the ground whilst that player's feet are still off the ground such that the player's head and/or upper body come into contact with the ground is dangerous play.
Sanction: Penalty kick
Sanction: Penalty kick
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