Declaration FIFA put out: Stateside lawyer against it (9)
I believe the answer is:
affidavit
'declaration' is the definition.
(I have seen 'Legal declaration' mean 'affidavit' so perhaps 'declaration' could also mean 'affidavit')
'fifa put out stateside lawyer against it' is the wordplay.
'put out' indicates an anagram.
'stateside lawyer' becomes 'DA' (short for district attorney, type of US lawyer).
'against' becomes 'v' (versus).
'fifa' with letters rearranged gives 'affi'.
'affi'+'da'+'v'+'it'='AFFIDAVIT'
(Other definitions for affidavit that I've seen before include "Sworn court statement" , "Legal declaration" , "Instrument's" , "Sworn written statement" , "Written declaration made under oath" .)