Yob in school finally excluded (4)
I believe the answer is:
lout
'yob' is the definition.
(both can mean an antisocial young man)
'school finally excluded' is the wordplay.
'finally' suggests the final letters.
'excluded' becomes 'out' (I've seen this in another clue).
The last letter of 'school' is 'l'.
'l'+'out'='LOUT'
'in' acts as a link.
(Other definitions for lout that I've seen before include "Ill-mannered or aggressive man" , "A noisy, badly behaved youth" , "A coarse ill-mannered fellow" , "'Buffoon, oaf (4)'" , "Oaf, hooligan" .)