Hares not running, in the main (5,3)
I believe the answer is:
north sea
'main' is the definition.
(North Sea is an example)
'hares not running' is the wordplay.
'running' indicates anagramming the letters (the letters run around to different places).
'hares'+'not'='haresnot'
'haresnot' is an anagram of 'NORTH SEA'.
'in the' is the link.
(Other definitions for north sea that I've seen before include "Expanse of water" , "Marine area off Britain" , "Part of the Atlantic between Britain and Scandinavia" , "(Formerly) German Ocean" , "Part of the Atlantic to the east of Great Britain" .)