Quickly disperse the poor outside the theatre (6)
I believe the answer is:
pronto
'quickly' is the definition.
(I've seen this before)
'disperse the poor outside the theatre' is the wordplay.
'disperse' indicates anagramming the letters (I've seen 'dispersing' mean this).
'outside' is an insertion indicator (some letters go outside others).
'the theatre' becomes 'NT' (National Theatre).
'poor' with letters rearranged gives 'proo'.
'proo' enclosing 'nt' is 'PRONTO'.
(Other definitions for pronto that I've seen before include "Right away, quickly" , "Quick as you can, amigo" , "Quickly, amigo" , "Right now, immediately" , "Quickly, immediately" .)