When the cars crashed, got bad chest abrasions (9)
I believe the answer is:
scratches
'bad chest abrasions' is the definition.
'scratches' can be an answer for 'abrasions' ('scratch' can be a synonym of 'abrasion'). I'm unsure of the 'bad chest' bit.
'when the cars crashed' is the wordplay.
'when' becomes 'sc' (I can't justify this - if you can you should give a lot more credence to this answer).
'crashed' indicates an anagram.
'the'+'cars'='thecars'
'thecars' is an anagram of 'ratches'.
'sc'+'ratches'='SCRATCHES'
'got' acts as a link.
Can you help me to learn more?
(Other definitions for scratches that I've seen before include "Abrasions" , "Withdraws" , "Abraded areas of the skin" , "opponents having no handicaps" .)