We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F-type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from the Tillinghast Reflector Echelle Spectrograph on the Fred Lawrence Whipple Observatory 1.5m telescope to determine the physical properties of this system. HAT-P-56b has a mass of 2.18M_J_, radius of 1.47R_J_, and transits its host star on a near-grazing orbit with a period of 2.7908day. The radius of HAT-P-56b is among the largest known for a planet with M_P_>2M_J_. The host star has a V-band magnitude of 10.9, mass of 1.30M_{sun}_, and radius of 1.43R_{sun}_. The periodogram of the K2 light curve suggests that the star is a {gamma} Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters.