Here , we present a kinematical analysis of the Virgo cluster ultra-diffuse galaxy ( UDG ) VCC 1287 based on data taken with the Keck Cosmic Web Imager ( KCWI ) . We confirm VCC 1287 ’ s association both with the Virgo cluster and its globular cluster ( GC ) system , measuring a recessional velocity of 1116 \pm 2 \mathrm { km s ^ { -1 } } . We measure a stellar velocity dispersion ( 19 \pm 6 \mathrm { km s ^ { -1 } } ) and infer both a dynamical mass ( 1.11 ^ { +0.81 } _ { -0.81 } \times 10 ^ { 9 } \mathrm { M _ { \odot } } ) and mass to light ratio ( 13 ^ { +11 } _ { -11 } ) within the half light radius ( 4.4 kpc ) . This places VCC 1287 slightly above the well established relation for normal galaxies , with a higher mass to light ratio for its dynamical mass than normal galaxies . We use our dynamical mass , and an estimate of GC system richness , to place VCC 1287 on the GC number – dynamical mass relation , finding good agreement with a sample of normal galaxies . Based on a total halo mass derived from GC counts , we then infer that VCC 1287 likely resides in a cored or low concentration dark matter halo . Based on the comparison of our measurements to predictions from simulations , we find that strong stellar feedback and/or tidal effects are plausibly the dominant mechanisms in the formation of VCC 1287 . Finally , we compare our measurement of the dynamical mass with those for other UDGs . These dynamical mass estimates suggest relatively massive halos and a failed galaxy origin for at least some UDGs .