Chiefly macho when getting out of line (6)
I believe the answer is:
mainly
'chiefly' is the definition.
(I know that chiefly can be written as mainly)
'macho when getting out of line' is the wordplay.
'macho' becomes 'main' (I can't explain this - if you can you should believe this answer much more).
'when' becomes 'e' (I've seen this in other clues).
'getting out of' suggests deleting specific letters.
'line' becomes 'ley' (as in ley lines).
'ley' with 'e' taken away is 'ly'.
'main'+'ly'='MAINLY'
Can you help me to learn more?
(Other definitions for mainly that I've seen before include "For the most part" , "Chiefly, principally" , "Generally or largely" , "Chiefly, largely" .)