Sheepish sort by some defensive wall (7)
I believe the answer is:
rampart
'defensive wall' is the definition.
(I know that rampart is a type of defensive wall)
'sheepish sort by some' is the wordplay.
'sheepish sort' becomes 'ram' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'by' means one lot of letters go next to another.
'some' becomes 'part' (only part of something).
'ram'+'part'='RAMPART'
Can you help me to learn more?
(Other definitions for rampart that I've seen before include "Defensive structure" , "Embankment built for defensive purposes" , "section of defence?" , "Bulwark, wall" , "Defensive wall or mound" .)