Guide's a good leader who was terrible climbing hill (9)
I believe the answer is:
navigator
'guide's' is the definition.
(I've seen this before)
'a good leader who was terrible climbing hill' is the wordplay.
I cannot quite see how this works, but
'a' is present in the answer.
'good' could be 'g' (abbreviation) and 'g' is found within the answer.
'hill' could be 'tor' (tor is a kind of hill) and 'tor' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for navigator that I've seen before include "reliable guide" , "sailor" , "crew member" , "One who plots a course" , "One directs the course, of a ship say" .)