Case of sow on heat, possibly -- a broad area (6)
I believe the answer is:
swathe
'a broad area' is the definition.
(I've seen this before)
'case of sow on heat possibly' is the wordplay.
'case of' means to remove the middle letters (outsides of).
'on' says to put letters next to each other.
'possibly' indicates anagramming the letters.
'sow' with its middle taken out is 'sw'.
'heat' with letters rearranged gives 'athe'.
'sw'+'athe'='SWATHE'
(Other definitions for swathe that I've seen before include "Broad strip or area of something" , "Row or path cut through" , "Wrap; a cut strip" , "Swaddle - cut strip" , "Row or path, of grass perhaps, when it is mown" .)