Its ruler? Al-za'im Qasim, early on! (4)
I believe the answer is:
over
'on' is the definition.
(over can mean on top of)
'its ruler? al-za'im qasim early' is the wordplay.
I cannot really see how this works, but
'ruler?' could be 'er' (short for Elizabeth Regina ie Queen Elizabeth) and 'er' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for over that I've seen before include "Rouond of six bowls in cricket" , "Six balls in cricket" , "Finished - across - in excess" , "end to radio communication?" , "Invalidate - upset" .)