We saw the lead up to this in shot 1209. Milan fullback Álex Jiménez (#74) made a somewhat desperate shot from the left of goal despite being surrounded by 2 Roma defenders. Here we see it cruising towards the goal, probably on target though it's difficult to tell from this angle, but there is no way that 2nd goalkeeper Pietro Boer is going to let it through.

In this shot, he is committed to his leap, but he is in perfect position to take care of business... And he does.