Xama45 was banned for using a flymod.
This is not allowed regarding the rules:
Do not cheat to get achievements or to mine blocks. This includes client-side scripts, mods, transparency texture packs or any other way that gives you an advantage over the standard and intended game play.
I made this even more clear now with the following update to the FAQ:
I have this client mod “x” that I want to install. Is that OK?
No. The only client side mods that are allowed are normal texture packs and a minimap that shows you your immediate surroundings. Texture packs that show you things that the normal texture does not show, are not allowed. All other modifications are not allowed either. No flying, speeding, no-clip (walking through walls), whatever it is – is not allowed.