Exasperate as caber tossed at Evans Head (8)
I believe the answer is:
acerbate
'exasperate' is the definition.
(I've seen this before)
'caber tossed at evans head' is the wordplay.
'tossed' indicates anagramming the letters.
'head' suggests taking the first letters.
The initial letter of 'evans' is 'e'.
'caber' with letters rearranged gives 'acerb'.
'acerb'+'at'+'e'='ACERBATE'
'as' acts as a link.
(Other definitions for acerbate that I've seen before include "distress" , "Exasperate" , "Put out" .)