It depends on the jurisdiction too, the law is different between countries and states within the same country. You also have to differeniate between criminal and civil liability. And you also have to weight that against the possibility someone will actually sue - just because they have the right doesn't actually mean they'll actually enforce it. They might actually want, say, a sound effect to get spread around even if they technically own the rights to it. And realistically, ligitation is expensive so you want to get your money back, and modders aren't exactly moneybags, so most for-free modders get a cease and desist letter at most (of course, this is not formal legal advice lol! - I'm sure if someone is unreprenentant they'll actually sue, but most modders stop at a C&D letter anyways). I mean, your mod isn't based around this sound effect, is it?