Connective tissue: mangle it when injured (8)
I believe the answer is:
ligament
'connective tissue' is the definition.
(I've seen this before)
'mangle it when injured' is the wordplay.
'when injured' indicates anagramming the letters (I've seen this in other clues).
'mangle'+'it'='mangleit'
'mangleit' anagrammed gives 'LIGAMENT'.
(Other definitions for ligament that I've seen before include "Tough band in joint" , "Fibrous connective tissue" , "What footballer may damage" , "Tissue which joins bones" , "it's the physical bond" .)