A defender may be surprised taken thus (5)
I believe the answer is:
aback
'be surprised taken thus' is the definition.
I can't tell whether this defines the answer.
'a defender' is the wordplay.
'defender' becomes 'back' (I've seen this before).
'a'+'back'='ABACK'
'may' acts as a link.
Can you help me to learn more?
(Other definitions for aback that I've seen before include "impeded by headwind?" , "One is surprised when taken thus" , "dismayed to be taken thus?" , "Sternwards" , "To take someone -- is to surprise them" .)