a toss-up

a toss-up

  (informal)
a situation where two or more possibilities are equally likely (often + between ) It's a toss-up between Angela and Moira for the editor's job. (often + whether ) It was a toss-up whether prices would go up or down.
References in periodicals archive ?
The latter is challenging sitting Senator Mark Udall (D-CO) in a toss-up race that could define whether Republicans take the Senate majority.