Man altered line (4)
I believe the answer is:
neil
'man' is the definition.
(man's name)
'altered line' is the wordplay.
'altered' indicates anagramming the letters.
'line' anagrammed gives 'NEIL'.
(Other definitions for neil that I've seen before include "- Armstrong, first man to set foot on the Moon" , "Boy" , "One of 14 DIAMONDS] 's" , "-- Sedaka, US singer" , "- Simon, US dramatist (Barefoot in the Park)" .)