Mania uncontrolled, learner becomes savage (6)
I believe the answer is:
animal
'savage' is the definition.
(I've seen this in another clue)
'mania uncontrolled learner' is the wordplay.
'uncontrolled' is an anagram indicator.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'mania' with letters rearranged gives 'anima'.
'anima'+'l'='ANIMAL'
'becomes' acts as a link.
(Other definitions for animal that I've seen before include "See 26" , "Creature having voluntary movement" , "Brute - one of the Muppets" , "Source of meat" , "Mammal" .)