Irritated socialist has one left (5)
I believe the answer is:
riled
'irritated' is the definition.
(I know that irritated can be written as riled)
'socialist has one left' is the wordplay.
'socialist' becomes 'red' (red can informally mean a socialist).
'has' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'left' becomes 'l' (common abbreviation).
'i'+'l'='il'
'red' going around 'il' is 'RILED'.
(Other definitions for riled that I've seen before include "Cross" , "Irritated, provoked" , "Annoyed" , "Made angry" , "get angry" .)