Take away cats Burt upset (8)
I believe the answer is:
subtract
'take away' is the definition.
(I've seen this in another clue)
'cats burt upset' is the wordplay.
'upset' indicates an anagram.
'cats'+'burt'='catsburt'
'catsburt' anagrammed gives 'SUBTRACT'.
(Other definitions for subtract that I've seen before include "Withdraw" , "Knock off" , "Take an amount away" , "Deduct" , "Take away (a number)" .)