Doorkeeper runs after hat (5)
I believe the answer is:
tiler
'doorkeeper' is the definition.
(I've seen this before)
'runs after hat' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'after' says to put letters next to each other.
'hat' becomes 'tile' (I've seen this before).
'r' after 'tile' is 'TILER'.
(Other definitions for tiler that I've seen before include "doorkeeper at lodge" , "High-level operator" , "Working man" , "Masons' doorkeeper" , "Roofer" .)