Maybe the French Open and US are to be rearranged (9)
I believe the answer is:
europeans
'maybe the french' is the definition.
(people from Europe)
'open and us are to be rearranged' is the wordplay.
'and' says to put letters next to each other.
'to be rearranged' indicates an anagram.
'us'+'are'='usare'
'open' put after 'usare' is 'usareopen'.
'usareopen' with letters rearranged gives 'EUROPEANS'.
(Other definitions for europeans that I've seen before include "Continentals" , "Frenchmen, Irishwomen, for instance" , "Irish and French people, say" , "The French and Italians, say" .)