I don't think that push on Romero was a yellow as you see it loads when a striker gives a defender a shove like that. but the 1st one below I wouldn't complain if was given as a yellow. Gifs below may take some time to load but most of this below is Thor'd from the ref thread.
As for the actual yellow he got, given the ref's position I can see why he thinks it's a yellow as Brobbey's elbow does catch Porro's chin, albeit not that hard. It was initially a free kick to us as Porro was all over the back of Brobbey but Brobbey is taking that ball all day long anyway. However yet again Brobbey grabs the shirt of a defender and then pushes his body back and moves his arm and his elbow must brush Porro's mush but nowt much in it but then helps shove Porro to the deck. Given the ref's position, viewing angle and watching in real-time speed then it's understandable how he can mistakenly see it as an elbow.
Brobbey ideally needs to cut down on shirt pulling as refs can see this more clearly unlike his strength of holding a player off. I think this is why he doesn't get as many fouls as some think he should. It's clear here that Brobbey has the strength even though Porro's is clambering all over him to get to the ball, unable to even move Brobbeyand Brobbey has the option of playing the ball as Porro is nowhere near.
Out of the 3, this is the one I'd book him for. Romero knows Brobbey is coming and tried to jump but Brobbey catches the side of Romero's left leg at the knee and also possibly hooks his foot. After he got booked he did seem to he keep a cool head the rest of the game and enjoyed Van de Ver getting booked.
