Struggle with siesta, upsetting the Spanish (7)
I believe the answer is:
wrestle
'struggle' is the definition.
(wrestling is a kind of struggling)
'with siesta upsetting the spanish' is the wordplay.
'with' becomes 'w' (abbreviation).
'siesta' becomes 'rest' (I've seen this in another clue).
'upsetting' says the letters should be written backwards.
'the spanish' becomes 'el' ('the' in Spanish).
'el' written backwards gives 'le'.
'w'+'rest'+'le'='WRESTLE'
(Other definitions for wrestle that I've seen before include "Fight - get to grips (with)" , "Grapple; strive" , "Fight in the ring" , "Struggle, grapple" , "Fight; struggle" .)