Even heartless crimes stopped by good standards (7)
I believe the answer is:
ensigns
'standards' is the definition.
(flags)
'even heartless crimes stopped by good' is the wordplay.
'heartless' says to hollow out the word (remove centre letters).
'crimes' becomes 'sins'.
'stopped by' means one lot of letters goes inside another (stopping can mean blocking a gap).
'good' becomes 'g' (abbreviation).
'even' with its middle removed is 'en'.
'sins' going around 'g' is 'signs'.
'en'+'signs'='ENSIGNS'
(Other definitions for ensigns that I've seen before include "Flags for naval officers" , "standards" , "US naval officers" , "Sensing (anag)" , "hauled up on deck?" .)