Facebook builds a profile of you based on what it perceives to be your interests, your location and your activity not just on Facebook but the entire internet. You don't have to search for something for Facebook to have an idea of who you are and what advertising and sponsored posts are appropriate for them to serve to you. Want to see how creepy Facebook is? Go to your settings and look for either "ads" or "ad preferences" (depending on whether you're using desktop or a phone app). You'll find everything Facebook has generated about you to serve you ads and sponsored posts. Sometimes it's way off or vague but more often than not it's spot on. Basically, if Facebook determines that you're a fan of sports and are from a certain location, that's when they should be serving sponsored posts for NRL games - but the clubs need to do their part to get the posts in front of you, too.