Bart tips off; "Small roles" (3,5)
'small roles' is the definition.
'bit parts' can be an answer for 'roles' (bit part is a kind of role). I am not sure about the 'small' bit.
'bart tips off' is the wordplay.
'off' is an anagram indicator.
'barttips' is an anagram of 'BIT PARTS'.
Can you help me to learn more?
(Other definitions for bit parts that I've seen before include "Small roles for actors", "Small roles in plays or films".)