It's just the typical mentality. He did absolutely nothing wrong yesterday and his positioning for a few balls over the top was excellent.
Even when he cut stuff out or did things well yesterday people screamed at him.
A guy near was calling him a ducking clown for not picking up a back pass!
Leaving the ground you could hear people bemoaning him.
It kicked off near me in the Family Stand (!) because someone berated Bravo in the first half when Otamendi headed the ball out for a throw. Someone rightly took exception, saying "how the fuck was that Bravo's fault?!" and it escalated from there with the stewards getting involved. He seems to polarise the fans more than any player, with the possible exception of Sterling.