From the guidelines: "If you think a story is spam or off-topic, flag it by clicking on its "flag" link. (Not all users will see this; there is a karma threshold.)"

"Off-Topic: Most stories about politics, or crime, or sports, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic."