Extremely silly to stop around Yemen's capital city (6)
I believe the answer is:
sydney
'city' is the definition.
(Sydney is an example)
'extremely silly to stop around yemen's capital' is the wordplay.
'extremely' suggests removing the centre.
'to stop' becomes 'end' ('end' can be a synonym of 'stop'**).
'around' says the letters should be written in reverse.
'capital' suggests taking the first letters.
'silly' with its centre removed is 'sy'.
The initial letter of 'yemens' is 'y'.
'end' backwards is 'dne'.
'sy'+'dne'+'y'='SYDNEY'
(Other definitions for sydney that I've seen before include "Australian port" , "Largest Australian city" , "First name" , "2000 Olympics hosts" , "opera house location" .)