TF, 15.6 applies to a specific event. That doesn't mean that other events are excluded the same rights. Ball in goal, on the ground. Any downward pressure from hand, arm or torso grounds the ball. Location or circumstance of the player not relevant unless a violation of law has occurred (such as offside). Try to the attackers, touch down to the defenders.
Very simple, the player is not taking possession of the ball or playing it in any other manner. Grounding is instantaneous and is ruled to occur first.
If the ball is in the air when contact is made by the player ... well, that's another thread.