be on the fence

To be unable or unwilling to commit to a decision or a side when presented with two opposing options or possibilities. The senator has been on the fence about the issue for years. You can't be on the fence about this—you need to choose between the two, now.

Also, straddle the fence. Be undecided, not committed, as in I don't know if I'll move there; I'm still on the fence, or He's straddling the fence about the merger. This picturesque expression, with its implication that one can jump to either side, at first was applied mainly to political commitments. [Early 1800s]

To be undecided or uncommitted. This term dates from the early nineteenth century and conjures up the image of a person who cannot or will not decide to which side of the fence to jump. At first the term was most frequently applied to politics—that is, which candidate or party one would support—and indeed it was even so defined in John Bartlett’s 1859 Dictionary of Americanisms: “Fenceriding: The practice of ‘sitting on the fence,’ or remaining neutral in a political contest until it can be seen ‘which way the cat is going to jump.’” Subsequently the term began to be applied to any kind of hedging.