Bony obstruction presents challenge (8)
I believe the answer is:
gauntlet
'challenge' is the definition.
(I've seen this in another clue)
'bony obstruction' is the wordplay.
'bony' becomes 'gaunt' (synonyms).
'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 "handy protection" , "Throw it down to offer a challenge" , "It may be thrown down or run" , "Strong glove, thrown down in challenge" , "that may be punishing for runner" .)