Made a mess of catching hammerhead, getting beaten (8)
I believe the answer is:
thrashed
'beaten' is the definition.
('thrash' can be a synonym of 'beat')
'made a mess of catching hammerhead' is the wordplay.
'made a mess of' becomes 'trashed' (to trash something is to make a mess of it).
'catching' is an insertion indicator.
'hammerhead' becomes 'h' (head letter of 'hammer').
'trashed' going around 'h' is 'THRASHED'.
'getting' is the link.
(Other definitions for thrashed that I've seen before include "Beaten soundly" , "severely punished" , "Beat violently" , "given whitewashing" , "Beat soundly" .)