Support broken by climbing ladder, holding post (6)
I believe the answer is:
tenure
'post' is the definition.
(thesaurus)
'support broken by climbing ladder' is the wordplay.
'support' becomes 'tee' (tee is a kind of support).
'broken by' indicates putting letters inside (inserted letters break into the word).
'climbing' is a reversal indicator (in a down clue, letters climb up).
'ladder' becomes 'run' (both can mean a tear in tights).
'run' back-to-front is 'nur'.
'tee' placed around 'nur' is 'TENURE'.
'holding' is the link.
(Other definitions for tenure that I've seen before include "Term for which to hold a position" , "Residence" , "Retune (anag.)" , "Neuter (anag)" , "Length of time a position is held" .)