Head off state tax at the outset (5)
I believe the answer is:
avert
'head off' is the definition.
(both can mean to prevent)
'state tax at the outset' is the wordplay.
'state' becomes 'aver' (both can mean to declare).
'at the outset' says to take the initial letters (the outset is the beginning).
The first letter of 'tax' is 't'.
'aver'+'t'='AVERT'
(Other definitions for avert that I've seen before include "Fend off" , "Parry" , "Obviate" , "Stave off" , "Head off" .)