Study article penned by Communist (4)
I believe the answer is:
read
'study' is the definition.
('read' can be a synonym of 'study')
'article penned by communist' is the wordplay.
'article' becomes 'a' (indefinite article).
'penned by' indicates putting letters inside.
'communist' becomes 'red' (red is a kind of communist).
'a' going within 'red' is 'READ'.
(Other definitions for read that I've seen before include "Interpret (text)" , "Understand written music" , "what follows 18 [OMASUM] in a 17 [RUMINANT]" , "Studied" , "Perused" .)