Incident balanced by head teacher (5)
I believe the answer is:
event
'incident' is the definition.
(an incident is an event or happening)
'balanced by head teacher' is the wordplay.
'balanced' becomes 'even' (I've seen this in another clue).
'by' is a charade indicator (letters next to each other).
'head' says to take the initial letters.
The initial letter of 'teacher' is 't'.
'even'+'t'='EVENT'
(Other definitions for event that I've seen before include "Significant happening" , "Happening, noteworthy perhaps" , "Occasion; sports contest" , "Result; incident" , "major incident" .)