Most bikes with vertical dropouts have some kind of retention cutouts, so that if the QR was properly installed (i.e. holds the wheel on when closed), the QR is

Most bikes with vertical dropouts have some kind of retention cutouts, so that if the QR was properly installed (i.e. holds the wheel on when closed), the QR is retained even when fully opened. You need to open it fully, then unscrew the cap a bit to make the nuts on both sides far enough apart to get outside the retention. I don't know if that is the case on the RadRunner 2, but it's the case on most road bikes with vertical dropouts.