City of the Spanish upset in agitation (6)
I believe the answer is:
toledo
'city' is the definition.
(I've seen this before)
'the spanish upset in agitation' is the wordplay.
'the spanish' becomes 'el'.
'upset' says the letters should be written backwards.
'in' indicates putting letters inside.
'agitation' becomes 'todo' (I've seen this before).
'el' backwards is 'le'.
'le' placed into 'todo' is 'TOLEDO'.
'of' is the link.
(Other definitions for toledo that I've seen before include "Spanish city famed for swords" , "Blade" , "historic Spanish city" , "Sp. city, former Visigoth and Castilian capital" , "Looted (anag) - Spanish city" .)