It's not round -- in fact, its rotation is chaotic, meaning that it doesn't rotate around a defined spin axis.
Found this on a fact sheet:
Hyperion is one of Saturn's smaller satellites and its elliptical orbit lies between that of Titan and Iapetus. Hyperion's low density indicates that the satellite is mainly composed of water-ice with a small amount of rocky material. The surface is covered with a darker material causing Hyperion to have a lower albedo compared to other icy moons.
Hyperion's shape is very irregular and it has been suggested that the satellite once was part of a larger object that was fractured by an impact in the distant past. Hyperion's surface also shows signs of heavy cratering with the largest crater approximately 120 km in diameter.
The orientation of Hyperion's axis of rotation is chaotic and unpredictable. The cause for the chaotic rotation could be due to the proximity of the large moon Titan, the ellipticity of Hyperions orbit and the 3:4 resonance between the orbital period of Titan and Hyperion.
bump--thanks for the post