Athlete crashing boat-car (7)
I believe the answer is:
acrobat
'athlete' is the definition.
(acrobat is a kind of athlete)
'crashing boat-car' is the wordplay.
'crashing' is an anagram indicator.
'boat'+'car'='boatcar'
'boatcar' anagrammed gives 'ACROBAT'.
(Other definitions for acrobat that I've seen before include "flipper" , "Rope-dancer" , "Athletic type" , "performer of risky feats?" , "Spectacular gymnast" .)