Shortened career over your foul (6)
I believe the answer is:
filthy
'foul' is the definition.
(I know that foul can be written as filthy)
'shortened career over your' is the wordplay.
'shortened' means to remove the last letter.
'career' becomes 'life' (career can mean someone's life or past).
'over' shows that the letters should be reversed in order.
'your' becomes 'thy' ('thy' historically meant 'your').
'life' with its last letter removed is 'lif'.
'lif' written backwards gives 'fil'.
'fil'+'thy'='FILTHY'
(Other definitions for filthy that I've seen before include "Obscene" , "Disgustingly dirty" , "Very dirty indeed" , "Really dirty, foul" , "Really dirty, disgusting" .)