Worry easing somehow surrounding Leader of Opposition (7)
I believe the answer is:
'worry' is the definition.
(I've seen this before)
'easing somehow surrounding leader of opposition' is the wordplay.
'somehow' indicates anagramming the letters.
'surrounding' is an insertion indicator.
'leader of' suggests taking the first letters.
The initial letter of 'opposition' is 'o'.
'easing' with letters rearranged gives 'agnise'.
'agnise' going around 'o' is 'AGONISE'.
(Other definitions for agonise that I've seen before include "rack" , "Be very worried" , "Be in torments of indecision" , "Undergo great anguish" , "worry a lot" .)