IMO greyling wasnt the one to blame for aaron smiths try, goosen was.
mere moments before smith recieved the ball and ran away to carve up the three Boks, goosen was right by the fringe of the ruck that smith darts down. goosen then looks to his left and quickly runs to add numbers on the backline, he then rdoes one hell of a basic schoolboy error, he runs with his back turned on the play.
while goosen is doing this, greyling looked to me to be running into the ruck (probably so he could forearm someone elses face), but unfortunately for greyling, the ball poped out for smith, who then did a roadrunner and left greyling sprawled all over the show, before adding flip (i think) and krichner to his highlight reel.
IMO if goosen was better aware of the situation, he would have called for numbers from his right to come over and aid the defence, before leaving the fringe with next to nobody there, but to turn his back on that ruck when play was still going, tsk tsk tsk, thats the experiecne factor i guess and something a player of his class will get right.
oh and thank u greyling, ur check from the NZRU should be arriving any day now, :P