Failure since employed by Grand Prix company (6)
I believe the answer is:
fiasco
'failure' is the definition.
(a fiasco is a failure or disaster)
'since employed by grand prix company' is the wordplay.
'since' becomes 'as' (both can mean 'because').
'employed by' means one lot of letters go next to another.
'grand prix' becomes 'FI' (Grands Prix are held in F1 or Formula 1 racing).
'company' becomes 'co' (abbreviation).
'as' after 'fi' is 'fias'.
'fias'+'co'='FIASCO'
(Other definitions for fiasco that I've seen before include "Sudden total disaster" , "Complete disaster" , "A debacle, complete mess" , "Debacle, a right mess" , "Calamity" .)