Aggressive chairman round church (5)
I believe the answer is:
macho
'aggressive' is the definition.
(I've seen this before)
'chairman round church' is the wordplay.
'chairman' becomes 'Mao' (Chinese leader Chairman Mao).
'round' is an insertion indicator.
'church' becomes 'ch' (common abbreviation).
'mao' enclosing 'ch' is 'MACHO'.
(Other definitions for macho that I've seen before include "Excessively male" , "Ultra-masculine" , "Jock" , "Affectedly virile" , "Exaggeratedly masculine" .)