for somebody getting pulled down from behind, here is what I would call.
It depends if there is another defender in the area getting ready to prevent an uncontested go at the keeper. If that was the only defender in the area, I would give a quick look around and let the play continue for 2-3 seconds until either a true advantage was acheived, or three is no advantage. A red card should have already been pulled out of the pocked so that everyone can see what the reaction of the referee is. Once the play is over, ie shot on goal, or no advantage is seen, the play is blown dead and the red card is given to the defender that pulled the person down. It gets goofy with the thought that you can't really let the play go on for more than 2-3 seconds without the reality setting in that after that much time has elapsed, you can't blow the whistle if you wait too long. You have that 2-3 seconds of opportunity to determine if an advantage situation exists. After that time has gone by, you have to let the play go until there is a stoppage in play for the card to be given.
Just my thoughts on the subject.
