Force needing support on “towpath case” (5)
I believe the answer is:
teeth
'force' is the definition.
(I've seen this before)
'support on towpath case' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'on' is a charade indicator (letters next to each other).
'case' means to remove the middle letters.
'towpath' with its middle taken out is 'th'.
'tee'+'th'='TEETH'
'needing' is the link.
(Other definitions for teeth that I've seen before include "Gearwheel cogs" , "symbols of legal power?" , "Force v" , "Dentition" , "Saw or gearwheel items" .)