On the back foot, finally abandoning sailor after baton’s whirled (6)
I believe the answer is:
dorsal
'on the back' is the definition.
'sailor after baton's whirled' is the wordplay.
'sailor' becomes 'sal' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' means one lot of letters go next to another.
'baton' becomes 'rod' (I've seen this before).
'whirled' shows that the letters should be reversed in order (in a down clue, letters go up).
'rod' back-to-front is 'dor'.
'sal' after 'dor' is 'DORSAL'.
'foot finally abandoning' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
(Other definitions for dorsal that I've seen before include "Fin on the back of marine vertebrates" , "Kind of fin" , "'On the back, a fin on a fish perhaps (6)'" , "On the upper back" , "(Of fin) on upper side" .)