Training causing serious injury when missing start (6)
I believe the answer is:
aiming
'training' is the definition.
('aim' can be a synonym of 'train')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for aiming that I've seen before include "Directing one's efforts" , "Pointing (a weapon)" , "Pointing, directing" , "Pointing towards a goal" , "Directing towards a goal" .)