You think?
Costa puts his left foot on de Vrij's calf, which is sliding past him at speed. It wasn't a foul and I don't *think* that Costa was trying to con the referee.
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Crystal clear penalty in my opinion. He had passed the defender and had a clear shot at goal
The fact the the defender (possibly) didn't intend to take him down doesn't change the fact that he did.
In any case the in game call would have been reasonable either way. Most certainly not a ref "mistake"