This is about a little game, in Dutch called: butter, cheese and eggs, don't ask me why,

and, if I'm right in English: tic tac toe. It's a 3*3 square and it's played by two players who write one by one a X or O in one of the squares. One of them uses X and the other O. A player has won if he/she has three X or O on one line, horizontal, vertical or diagonal.
Just in the situation of this riddle there are two rules:
1 If a player has a possibillity to get three on a line he/she
must do that.
2 If a player has a possibillity to prevent the other player to get three on a line, he/she
must do that.
Of course rule 1 is before 2.
In this situation each player has done three turns, this way:
O O .
O X .
X X .
It is quite obvious that the player who's turn it is will win. The question is, who's turn it is, and why.