A defender may be surprised taken so (5)
I believe the answer is:
aback
'surprised taken so' is the definition.
'aback' can be an answer for 'surprised' (I've seen this before). I'm unsure of the 'taken so' bit.
'a defender' is the wordplay.
'defender' becomes 'back' (left-backs and right-backs are football defenders).
'a'+'back'='ABACK'
'may be' acts as a link.
Can you help me to learn more?
(Other definitions for aback that I've seen before include "(Taken) by surprise" , "To take someone -- is to surprise them" , "dismayed to be taken thus?" , "Towards the rear (arch.)" , "One is surprised when taken thus" .)