Force, extremely tough, after support on course (5)
I believe the answer is:
teeth
'force' is the definition.
(I've seen this before)
'extremely tough after support on course' is the wordplay.
'extremely' says to hollow out the word (remove centre letters).
'after' means one lot of letters go next to another.
'support on course' becomes 'tee' (golf tee on a golf course).
'tough' with its centre taken out is 'th'.
'th' after 'tee' is 'TEETH'.
(Other definitions for teeth that I've seen before include "Choppers" , "Incisors maybe" , "Structures in the jaws" , "symbols of legal power?" , "genuine power" .)