A common idea to promote a race is to encourage people to share on Facebook. The caution is that Facebook policy prohibits you from offering incentives to do this. See https://developers.facebook.com/policy/ – Part 4 and paragraph 5 (as of this writing):
“Only incentivize a person to log into your app, enter a promotion on your app’s Page, or check-in at a place. Don’t incentivize other actions.”
While a number of customers have requested that we offer a way to incentivize people who share the fact they registered on Facebook, we do not because of this Facebook rule. There is a huge risk that Facebook would shut down our API and shut down customer Facebook Pages.
So we will continue to just offer our standard Facebook Share capability when people look at a race or when they sign up for a race.