Stealing some company car, I promptly retired (6)
I believe the answer is:
piracy
'stealing' is the definition.
(I know that piracy is a type of hijacking)
'some company car i promptly retired' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'retired' says the letters should be written backwards.
'ycarip' is hidden within 'company car i promptly'.
'ycarip' written backwards gives 'PIRACY'.
(Other definitions for piracy that I've seen before include "Copyright infringement" , "Illegal copying" , "Robbery on the high seas" , "Robbing of ships at sea" , "Act of plagiarism" .)