Falter for a second, then fall (7)
I believe the answer is:
stumble
'falter' is the definition.
(I know that falter can be written as stumble)
'second then fall' is the wordplay.
I cannot really see how this works, but
'second' could be 's' (common abbreviation) and 's' is found in the answer.
'fall' could be 'tumble' (synonyms) and 'tumble' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'for a' is the link.
Can you help me to learn more?
(Other definitions for stumble that I've seen before include "blunder" , "Fall while walking or running" , "Come near to falling while walking" , "Momentarily trip" , "Miss a step and risk falling" .)