Shut up about unusually grey play by Ibsen (4,4)
I believe the answer is:
peer gynt
'play by ibsen' is the definition.
(I've seen this before)
'shut up about unusually grey' is the wordplay.
'shut up' becomes 'pent' ('pent' can be a synonym of 'shut up'**).
'about' is an insertion indicator.
'unusually' indicates an anagram.
'grey' is an anagram of 'ergy'.
'pent' placed around 'ergy' is 'PEER GYNT'.
(Other definitions for peer gynt that I've seen before include "Titled hero" , "Ibsen play (for which Grieg wrote music)" , "(Son of Ase in) Ibsen play" , "Norse legend" , "Ibsen drama" .)