It all happened during a match between Russians Anna Kalinskaya and Anastasia Potapova with one of the players complaining to the umpire about it. The fan in question was sitting silently in the stand watching with a Ukrainian flag and a vinok (floral wreath crown) on her head breaking no rules.
After the players complained the umpire confronted the fan saying 'its not nice to sit with the flag' to which the fan, whose name is Lola, responded that it's not nice to invade a country. The security marshal became aggressive towards the fan asking her to leave the court with some spectators stepping in on her behalf. Not wanting to create a scene, Lola stood up and left the court.
About 20 minutes later she was approached by the head of security on the complex telling her that she is breaking a rule by displaying a flag of inappropriate size. As tennis journalist Ben Rothenberg pointed out, it's a rule that has never been enforced seriously with many full-sized flags being displayed on the stands for years.
Lola was forced to store the flag in her car after which she was allowed to return to the grounds. Asked to comment on the matter, the event simply pointed out the rule with the WTA remaining silent. The players and the umpire haven't responded to reporters asking for a comment.