Collided with back of enormous goods vehicle (6)
I believe the answer is:
struck
'collided' is the definition.
(I've seen this before)
'with back of enormous goods vehicle' is the wordplay.
'with' means one lot of letters go next to another.
'back of' indicates one should take the final letters.
'goods vehicle' becomes 'truck' (I've seen this before).
The last letter of 'enormous' is 's'.
's'+'truck' is 'STRUCK'.
(Other definitions for struck that I've seen before include "Punched" , "dismantled" , "Thumped" , "Made to pause by something unexpected" , "set out" .)