Attend a soldier's party and make a run for it (4,1,7)
I believe the answer is:
beat a retreat
'make a run for it' is the definition.
'attend a soldier's party' is the wordplay.
'attend' becomes 'beat' (I've seen this in other clues).
'soldier' becomes 're'.
'party' becomes 'treat' (I've seen this before**).
'beat'+'a'+'re'+'treat'='BEAT A RETREAT'
'and' is the link.
(Other definitions for beat a retreat that I've seen before include "Retire hastily" , "Withdraw to avoid something unpleasant" , "Withdraw quickly" , "Depart hastily" , "Go away in a hurry" .)