New threat involving English playhouse (7)
I believe the answer is:
'playhouse' is the definition.
(I know that playhouse can be written as theatre)
'new threat involving english' is the wordplay.
'new' indicates an anagram.
'involving' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'threat' anagrammed gives 'thatre'.
'thatre' going around 'e' is 'THEATRE'.
(Other definitions for theatre that I've seen before include "where Finney played" , "war zone" , "Drama venue" , "Building for dramatic art" , "Place for spectacles" .)