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 am not certain 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" .)