Leapt sideways at first before car crash (6)
I believe the answer is:
sprang
'leapt' is the definition.
(springing is a kind of leaping)
'sideways at first before car crash' is the wordplay.
'at first' suggests taking the first letters.
'before' says to put letters next to each other.
'car crash' becomes 'prang' (I've seen this before).
The initial letter of 'sideways' is 's'.
's'+'prang'='SPRANG'
(Other definitions for sprang that I've seen before include "got out of jail" , "freed prisoner" , "Leaped forward" , "released from prison" , "Lept forward" .)