Fight as expected by back of school (4)
I believe the answer is:
duel
'fight' is the definition.
(duel is a kind of fight)
'expected by back of school' is the wordplay.
'expected' becomes 'due' (I've seen this before).
'by' means one lot of letters go next to another.
'back of' says to take the final letters.
The last letter of 'school' is 'l'.
'due'+'l'='DUEL'
'as' is the link.
(Other definitions for duel that I've seen before include "Potentially fatal fight between two people" , "One got satisfaction from this" , "Two-person combat" , "Arranged fight" , "Prearranged engagement" .)