Revolutionary painting? Very upset: it’s hard work (7)
I believe the answer is:
travail
'hard work' is the definition.
(travail can mean hard work or effort)
'revolutionary painting? very upset' is the wordplay.
'revolutionary' says the letters should be written in reverse.
'painting?' becomes 'art' (painting is an art).
'very' becomes 'v' (abbreviation).
'upset' becomes 'ail' (I've seen this before).
'art' written backwards gives 'tra'.
'tra'+'v'+'ail'='TRAVAIL'
'it's' acts as a link.
(Other definitions for travail that I've seen before include "painful exercise" , "Old word for pangs of childbirth" , "Painful labour" , "Labour, toil" , "Toil - anguish" .)