Injury largely was responsible for career (6)
I believe the answer is:
hurtle
'responsible for career' is the definition.
'hurtle' can be an answer for 'career' (I've seen this before). I am not sure about the 'responsible for' bit.
'injury largely' is the wordplay.
'injury' becomes 'hurt' (synonyms).
'largely' becomes 'le' (I can't justify this - if you can you should give a lot more credence to this answer).
'hurt'+'le'='HURTLE'
'was' is the link.
Can you help me to learn more?
(Other definitions for hurtle that I've seen before include "Move rapidly or fall headlong" , "Rush violently" , "Dash, move at high speed" , "Dash, move rapidly" , "Lacking speed" .)