Strapping damaged leg and arm mostly (5)
I believe the answer is:
large
'strapping' is the definition.
(I've seen this before)
'damaged leg and arm mostly' is the wordplay.
'damaged' is an anagram indicator.
'and' means one lot of letters go next to another (I've seen this in other clues).
'mostly' means to remove the last letter.
'arm' with its final letter removed is 'ar'.
'leg' after 'ar' is 'arleg'.
'arleg' is an anagram of 'LARGE'.
(Other definitions for large that I've seen before include "Big, almost regal" , "Big - 5 down (anag)" , "Immense" , "Elgar (anag)" , "substantial" .)