Mania uncontrolled, student becomes beast (6)
I believe the answer is:
animal
'beast' is the definition.
(a beast is an animal)
'mania uncontrolled student' is the wordplay.
'uncontrolled' is an anagram indicator.
'student' becomes 'l' (as in L-plates for learner drivers).
'mania' is an anagram of 'anima'.
'anima'+'l'='ANIMAL'
'becomes' acts as a link.
(Other definitions for animal that I've seen before include "Organism having life" , "Brutal, sensual" , "Uncivilised person" , "One sharing our kingdom" , "Circus performer, maybe" .)