Find Leo upset about a pet (6)
I believe the answer is:
locate
'find' is the definition.
(I know that find is the is a more specific form of the action of locate.)
'leo upset about a pet' is the wordplay.
'upset' indicates an anagram.
'about' means one lot of letters goes inside another.
'a pet' becomes 'cat' (cats are often kept as pets).
'leo' anagrammed gives 'loe'.
'loe' enclosing 'cat' is 'LOCATE'.
(Other definitions for locate that I've seen before include "Find out where something is" , "Pinpoint the position" , "Pinpoint in Alecto" , "Put in place" , "Find, or establish in particular place" .)