A communist protects last of them with weapons (5)
I believe the answer is:
armed
'with weapons' is the definition.
(I've seen this before)
'a communist protects last of them' is the wordplay.
'communist' becomes 'red' (red is a kind of communist).
'protects' indicates putting letters inside.
'last of' suggests the final letters.
The final letter of 'them' is 'm'.
'red' going around 'm' is 'rmed'.
'a'+'rmed'='ARMED'
(Other definitions for armed that I've seen before include "Supplied with weapons" , "Gave weapon" , "Equipped with weapons" , "Munitioned" , "with Browning?" .)