Bewilder a six-footer about to get a sum wrong (6)
I believe the answer is:
bemuse
'bewilder' is the definition.
(synonyms)
'a six-footer about to get a sum wrong' is the wordplay.
'a six-footer about' becomes 'bee' (I can't explain this - if you can you should give a lot more credence to this answer).
'to get' means one lot of letters goes inside another.
'wrong' is an anagram indicator.
'sum' with letters rearranged gives 'mus'.
'bee' enclosing 'mus' is 'BEMUSE'.
Can you help me to learn more?
(Other definitions for bemuse that I've seen before include "Puzzle, make confused" , "Confuse, bewilder" , "Cause puzzlement" , "Fox" , "Muddle or stupefy" .)