The best thing is to first look for a professional piercing shop, or go to the shop where you had pierced your ears and ask them if they have clear retainers for your ears. These can help in hiding the piercing. Find more tips here http://www.ehow.com/how_4422266_hide-piercing.html.
Get one of those little circle bandaids and put it over your ear. As an extra precaution also do like someone else said and pull your hair down a little further in that side. Another thing you can do is wear a big clothe headband and it would look like your holding your hair back, but you could also cover your ear with it.
I just put tape over mine and the refs are fine with it. But some of my friends put a big headband over the tops of their ears or put their hair up and cover the top of their ears. I think the refs would be ok with just taping it though.