Just today i was playing in a game of casual mode, and i noticed someone who was a level 76 on the other team and had an onyx medal. After that I left and started another match and this one had someone who was level 12 but had an onyx medal. I left that game and joined another just to find a level 54. Now I don't know what level you get booted out of casual mode but i think it should be less than 20.