https://rpg.stackexchange.com/ is a stack dealing with table top RPG games, the most prominent being Dungeons and Dragons (D&D). Answering questions almost always relies on information from rule books sold by the makers of D&D.
Due to stack culture reasons, answers directly referencing the rules are valued far more than experienced perspectives. To avoid link rot, it is essentially a requirement to copy-paste the relevant portions of the rules into the answer. These portions could be a few sentences, or even a few paragraphs, often they are the entire rules for a spell or character ability.
Even answers that do not directly quote the rule books often use information from those rulebooks to write an answer.
Ultimately SE is using this content to turn a profit, so we can't naively think we are merely sharing information with friends and are immune to copyright law. Are we actually allowed to share this pay-walled information? To what extent is this kind of content infringing copyright? What should we be looking out for to prevent issues?