As usual, I agree with Peter
Never a pen, ask yourself what MacAllister was doing there. He didn't try to head the ball, control the ball or position himself to get control of the ball. He ran towards Duko while Duko was trying to clear the ball and stood there, directly in front of him. Then when the follow through brushed him he flung himself to the ground screaming.
Yellow for diving
But more importantly, since when did it become acceptable for defenders to grab anyone in the box when a cross is played in and drag them to the ground?! Brentford did it all game long, at one point someone dragged White into the goal as the cross came in!
It's currently a free for all on set pieces. Defenders seem to be able to do anything and get away with it.
I just hope we're doing it as well.