What do athletes need to do after they get there belly button pierced?

I would suggest you get a PTFE barbell for your navel piercing and wear that for as long as your sports schedule lasts. PTFE is a biocompatible surgical Teflon that will flex with movement and prevent any damage from occurring during contact play, that in concert with taped gauze over the piercing and you should be good to go. Standard jewellery (barbells and rings) don't like impacts and is very rough on the new piercing when it's trying to heal. Getting the piercing sooner than the season start would have been the better bet but for now consider the PTFE as your best option. See your professional body piercer for more assistance.