Realistically, I think the vast majority of us who shout stuff at matches would cack ourselves a bit if confronted by the person we were shouting at, even if it was someone like Louis Reed or Stefan Scougall.
Most fans are guilty of shouting 'That was fucking wank' or 'Thas bin shite today [insert name here]'. I can say with 100% certainty that I am. But can you imagine if the player you were gobbing at actually came up to your face and questioned you on the things you were shouting?
People go on about the protection of anonymity on social media, meaning people get brave and say shit they'd never say to someone's face, but the same is massively true for crowds as well. If the match was on and the other 30,000 fans weren't drowning out your insults, would you say half the things you usually say at a match? Even if it was pretty likely that McBurnie or Lundstrum might 'do a Dier' and come up to have a word about why you think it's acceptable to call them a useless wanker whilst at work?
Obviously I know this is different from what happened last night. Sounds like some brainless turds were having a pop at Dier's brother so he waded in. Just found it an interesting thing to think about.