Go for the man protecting one (3)
I believe the answer is:
hie
'go' is the definition.
(hiing is a kind of going)
'the man protecting one' is the wordplay.
'the man' becomes 'he'.
'protecting' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral**).
'he' placed around 'i' is 'HIE'.
'for' acts as a link.
(Other definitions for hie that I've seen before include "make haste" , "Hurry" , "Be quick (lit.)" , "Hasten" , "Make one's way quickly" .)