If we're going to discuss rules questions, we'll often be quoting from the rule books, in part because Stack Exchange really encourages quoting from a source instead of (and in addition to) just linking to it.
In a recent question, we have an entire paragraph quoted from the MLB rulebook (which is copyrighted). I'm not too concerned with what we've done for this individual question, but for the longer term: after a few seasons of people asking baseball rules questions, we can end up with a significant portion of the MLB rulebook quoted here. At some point, after a large portion of the rulebook (if not the whole thing) can be reassembled from quotes on sports.stackexchange, will there be a copyright violation? If so, it would be nice to address the issue now, while the scope is smaller.
(I'm writing this from a US perspective on copyright law because the copyright holder of this particular rulebook is in the US and because Stack Exchange is based in the US. So this specific issue is US-centric, but the general question is still probably applicable to the rest of the world.)