Bony obstruction presents a challenge (8)
I believe the answer is:
gauntlet
'a challenge' is the definition.
(thesaurus)
'bony obstruction' is the wordplay.
'bony' becomes 'gaunt' ('gaunt' can be a synonym of 'bony').
'obstruction' becomes 'let' (I've seen this in other clues).
'gaunt'+'let'='GAUNTLET'
'presents' acts as a link.
(Other definitions for gauntlet that I've seen before include "Long-sleeved glove" , "Throw it down to offer a challenge" , "Throw this glove down as a challenge" , "outdated military punishment" , "Iron glove" .)