Leo Messi's finish secured by left leg (4)
I believe the answer is:
lion
'leo' is the definition.
(I've seen this in another clue)
'messi's finish secured by left leg' is the wordplay.
'finish' says to take the final letters.
'secured by' is an insertion indicator (inserted letters are held or secured).
'left' becomes 'l' (common abbreviation).
'leg' becomes 'on' (cricket term, fielding positions).
The final letter of 'messi' is 'i'.
'l'+'on'='lon'
'i' put within 'lon' is 'LION'.
(Other definitions for lion that I've seen before include "Carnivorous 6" , "Leo" , "Important figure" , "The -, the Witch and the Wardrobe" , "Courageous person" .)