Nasty ruffian collars school waif (10)
I believe the answer is:
ragamuffin
'waif' is the definition.
(I've seen this before)
'nasty ruffian collars school' is the wordplay.
'nasty' indicates anagramming the letters.
'collars' means one lot of letters goes inside another (to collar can mean to apprehend or capture).
'school' becomes 'gam' (I've seen this in other clues).
'ruffian' is an anagram of 'rauffin'.
'rauffin' going around 'gam' is 'RAGAMUFFIN'.
(Other definitions for ragamuffin that I've seen before include "Street child" , "Tatterdemalion" , "Waif" , "little scruff" , "One got up badly" .)