The ol' non-FIFA-sanctioned indoor football refs always tell you that you can't tackle from behind at all, but then proceed to ignore there own rules most of the time. Not really relevant but it annoys me - it's just a lottery as to whether the ref will call a hack to the ankles from the back of the player a foul or not.
Exactly why Indoor soccer is non sanctioned - its just made up mumbo jumbo.
Futsal on the other hand ..