Mild chap the Spanish turned up (6)
I believe the answer is:
gentle
'mild' is the definition.
('gentle' can be similar in meaning to 'mild')
'chap the spanish turned up' is the wordplay.
'chap' becomes 'gent' (I've seen this in other clues**).
'the spanish' becomes 'el'.
'turned up' says the letters should be written backwards.
'el' back-to-front is 'le'.
'gent'+'le'='GENTLE'
(Other definitions for gentle that I've seen before include "Mild, moderate" , "Kind, not rough" , "Mild and benign" , "'Mild, soft, tender (6)'" , "Mild-mannered" .)