Performing animal outside in (5)
I believe the answer is:
doing
'performing' is the definition.
('do' can be a synonym of 'perform')
'animal outside in' is the wordplay.
'animal' becomes 'dog' (type of animal).
'outside' means one lot of letters goes inside another.
'dog' enclosing 'in' is 'DOING'.
(Other definitions for doing that I've seen before include "thrashing" , "Engaged in -- active" , "Making" , "Hoaxing" , "Impersonating" .)