"Ball's in the air."

Jannie du Plessis charges at the Stormers and is tackled.

François Louw of the Stormers plays the ball. Clearly he releases Du Plessis and then plays the ball.

The referee penalises Louw and sends him to the sin bin.

Louw's plea in mitigation is based on his belief that the ball was in the air.

Ball in the air does not mean that there has not been a tackle.
Ball in the air does not exonerate the tackler from allowing the tackled player to play the ball.
Ball in the air does not mean thataa player not on his feet is allowed to play the ball.

Louw goes down off his feet. When  he is off his feet he has no right to play the ball. He did play the ball. The referee was right to penalise him.

The yellow card was for repeated infringements by the Stormers who had been penalised six times at tackles before this infringement.