Flounder leads to small fall (7)
I believe the answer is:
stumble
'flounder' is the definition.
(thesaurus)
'small fall' is the wordplay.
I cannot quite see how this works, but
'small' could be 's' (abbreviation - e.g. clothes size) and 's' is present in the answer.
'fall' could be 'tumble' (tumbling is a kind of falling) and 'tumble' is found within the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
'leads to' acts as a link.
Can you help me to learn more?
(Other definitions for stumble that I've seen before include "Come near to falling while walking" , "Slip - fall" , "Falter" , "Fall while walking or running" , "Momentarily trip" .)