Beats a retreat, protecting ruler (4)
I believe the answer is:
tsar
'ruler' is the definition.
(tsar is a kind of ruler)
'beats a retreat protecting' is the wordplay.
'protecting' says the answer is hidden in the clue.
'TSAR' is hidden in the letters of 'beats a retreat'.
(Other definitions for tsar that I've seen before include "Alexander and Nicholas held this title in Russia" , "Person in charge" , "specific authority" , "Eg, Ivan the Terrible" , "Monarch of old Russia" .)