Midget's mouth treated by doctor after end of fight (3,5)
I believe the answer is:
tom thumb
'midget's' is the definition.
(Tom Thumb is an example)
'mouth treated by doctor after end of fight' is the wordplay.
'treated' indicates an anagram.
'by' says to put letters next to each other.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus**).
'after' means one lot of letters go next to another.
'end of' indicates one should take the final letters.
The final letter of 'fight' is 't'.
'mouth' anagrammed gives 'omthu'.
'omthu'+'mb' is 'omthumb'.
'omthumb' put after 't' is 'TOM THUMB'.
(Other definitions for tom thumb that I've seen before include "Diminutive folk hero" , "Little fellow" , "Very little chap of English folklore" , "Notably small person" , "Panto character" .)