Sunk at the end of round one (6)
I believe the answer is:
undone
'sunk' is the definition.
(I know that sunk can be written as undone)
'at the end of round one' is the wordplay.
'at' means one lot of letters go next to another.
'of' becomes 'o''.
'round' indicates an anagram.
'one' becomes 'un' (northern English dialect form of 'one').
'end'+'o'='endo'
'endo' is an anagram of 'done'.
'done' put after 'un' is 'UNDONE'.
(Other definitions for undone that I've seen before include "Unfastened or brought to ruin" , "Ruined - no longer fastened" , "Not finished; untied" , "Opened" , "Brought to ruin or buttons not fastened" .)