New threat involving English playhouse (7)
I believe the answer is:
Here is my best explanation:
'playhouse' is the definition.
(I've seen this before)
'new threat involving english' is the subsidiary indication.
'new' indicates anagramming the letters.
'involving' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'threat' is an anagram of 'thatre'.
'thatre' going around 'e' is 'theatre'.
(Other definitions for theatre that I've seen before include "where they're in action?", "Field of operations", "Playhouse or sphere of action", "Where dramas may be", "Playhouse - operations room", "Place for stage works", "Building for plays or operations", "Space for dramatic art and surgery", "Place where plays are produced" and "Play venue".)