Mêlée cut short small investigation (8)
I believe the answer is:
scrutiny
'investigation' is the definition.
(I know that scrutiny is a type of investigation)
'melee cut short small' is the wordplay.
'melee' becomes 'scrum' (both can mean a group of people fighting).
'cut short' means to remove the last letter.
'small' becomes 'tiny' (similar in meaning).
'scrum' with its final letter removed is 'scru'.
'scru'+'tiny'='SCRUTINY'
(Other definitions for scrutiny that I've seen before include "City runs (anag.)" , "Critical examination" , "From close inspection" , "Close investigation" , "Intense study" .)