Cast admitting exhausted ensemble is a sensation (7)
I believe the answer is:
feeling
'sensation' is the definition.
(I've seen this before)
'cast admitting exhausted ensemble' is the wordplay.
'cast' becomes 'fling' (both can mean to throw).
'admitting' indicates putting letters inside (admit can mean to welcome in or accept).
'exhausted' means to remove the middle letters (the word is emptied out or exhausted).
'ensemble' with its middle removed is 'ee'.
'fling' enclosing 'ee' is 'FEELING'.
'is a' acts as a link.
(Other definitions for feeling that I've seen before include "Sensation" , "Sense, emotion" , "Emotion; opinion" , "Sympathy" .)