Many times I've seen people throw the front half of their tallis katan over their shoulder so that it doesn't get in their way. Mostly teenagers playing sports or people doing something that might get it dirty. This way, the hole of the tallis katan is still around their neck, but now both halves of the beged are hanging in the back.
Is this considered "wearing" tzitzis? According to whom?
(This is an issue, since nowadays one is obligated to wear tzitzis all the time (Igros Moshe OC 4:4). Other possible nafkei minah: Making a brocha again if one didn't intend to "fix" it, but does. If the beged is put on l'chatchila this way, does one make a brocha. Walking 4 amos without tzitzis.)