I have not read the book and the recent TV show is sitting in my to watch pile so I can not help much on that front, I will also have to avoid the argue from summary stuff for now as I do want to watch the TV show. As for social justice in the modern sense it seems to mean many things to many people. At its core it seems to be a revisit of the old ran out of the village concept -- 600 years ago if you were booted out of the village it would likely not end too well for you. It kind of lived on in certain professional organisations (finance has a whole bunch of blacklisted traders and practitioners, the law has things like bar associations and the military is a whole world unto itself, though that can be tricky to dissect unless you are a lawyer and varies somewhat by country -- the US has the uniform code of military justice which I find to be very odd at times). Anyway though laws say many things you can follow the laws to the letter and still be an arsehole, however you have to live in society and if you are ostracised from that your life can still be hard (if people actively avoid buying my services or products because I am a bellend then I suffer even if I have technically committed no crime*, ditto if nobody wants to help me out).
Today I probably can not pick my neighbours more than two houses either side of me out of a lineup (and I live in a town of less than 150K people). However I am on the internet in various guises and can be troubled there which brings up to the modern day when people on various social networks and related concepts can try to make my internet life harder, or indeed take it back to the real world and trouble me there.
*or committed a crime but either got away with it after some fashion, see also "everybody knows he did it".
So yeah when someone suffers action by a community because of something they did, criminal or otherwise, or people think they did (there are no shortage of people getting things very wrong, see also why vigilantism is discouraged and there are rules of evidence and investigation and such like for police) it would be an example of social justice. It can also happen where a community has differing beliefs from the individual.