Exasperated supporters regularly speed away (7,3)
I believe the answer is:
brassed off
'exasperated' is the definition.
(I've seen this before)
'supporters regularly speed away' is the wordplay.
'supporters' becomes 'bras' (I've seen this in other clues).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'away' becomes 'off' ('off' can be a synonym of 'away'**).
The alternate letters of 'speed' are 'sed'.
'bras'+'sed'+'off'='BRASSED OFF'
(Other definitions for brassed off that I've seen before include "Exasperated" , "Fed up" .)