Scoundrel crashes cars by a lake (6)
I believe the answer is:
rascal
'scoundrel' is the definition.
(I know that rascal is a type of scoundrel)
'crashes cars by a lake' is the wordplay.
'crashes' indicates anagramming the letters.
'by' says to put letters next to each other.
'lake' becomes 'l' (geographical abbreviation).
'cars' anagrammed gives 'rasc'.
'rasc'+'a'+'l'='RASCAL'
(Other definitions for rascal that I've seen before include "Cheeky person, scamp" , "Knave, rogue" , "Impudent child" , "Michievous person/child" , "Villain" .)