Yes it is possible to earn bitcoin while playing game, you can search through google there are many sites now that support that, but you need to read their FAQ and reviews before you register and play because every site has different rules you regulations so be always careful. Some will make you deposit bitcoin before you can play or some will make you put or credit card, mostly this kind of sites do have a specific BTC that you can withdraw before you can cash it out same as gambling. So Good luck and be careful.