Quote Originally Posted by Blackberry View Post
Here's what I reckon. Whether or not a player on the ground can play the ball depends on how he got to there; if he's on the ground following a tackle, he cannot play it, if he's on the ground for any other reason, he can play it. The OP's scenario did not involve a tackle so the player was OK.
Well, exception in law 15.6 (quoted above) tells the opposite:
Exception: Ball goes into the in-goal. After a tackle near the goal line, if the ball has been released and has gone into the in-goal any player, including a player on the ground, may ground the ball

I'm with Marauder when he says:
Grounding is instantaneous and is ruled to occur first.

My 2 cents,