Its not a red if seen in isolation but when you look at what happened as an entirety, Sons tackle caused the broken leg. Its from behind, Gomes cant react to it hence why hes off balance before being clobbered again by Aurier. You cant go about on a football pitch clipping people from behind and expect to get away with it. At some point an injury will happen. It was a snide foul, deliberate and happened because of the minute or twos play before the tackle. Doesnt matter whether he meant to break his leg or not, fact is his tackle did. Had he not been such a [Poor language removed] and had a go from behind, no broken leg.
Circumstance is circumstance, Gomes is unlucky, 99/100 he gets up from that and a yellow card is enough. Dont give a turd about Son and how upset he is, id be raging at him if that happened to me or any of my teammates. He should be getting shown up for being the little shithows he is instead of all this "hes not the type of player rubbish". You get in a fight, punch someone and they bang their head on the floor and dies, doesnt matter whether you meant to kill them or not.