Football team left opening behind last of defenders (10)
I believe the answer is:
portsmouth
'last of defenders' is the definition.
The definition suggests a singular noun which matches the answer.
'football team left opening behind' is the wordplay.
I cannot really see how this works, but
'left' could be 'port' (left side of a ship - opposite of starboard) and 'port' is located in the answer.
'opening' could be 'mouth' (mouth is a kind of opening) and 'mouth' is found within the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for portsmouth that I've seen before include "naval base" , "South coast city" .)