Showing sign of injury, having lost heart, being frightened (6)
I believe the answer is:
scared
'being frightened' is the definition.
(scared means frightened or fearful)
'showing sign of injury having lost heart' is the wordplay.
'showing sign of injury' becomes 'scarred' (having a scar).
'having lost heart' says to hollow out the word (remove centre letters).
'scarred' with its centre taken out is 'SCARED'.
(Other definitions for scared that I've seen before include "Nervous" , "Afraid, anxious" , "Frightened, alarmed" , "having kittens" , "Frightened or intimidated" .)