  We present photometry and spectroscopy of the peculiar TypeII supernova (SN)
2010jp, also named PTF10aaxi. The light curve exhibits a linear decline with a
relatively low peak absolute magnitude of only -15.9, and a low radioactive
decay luminosity at late times that suggests a nickel mass below 0.003
$M_{\odot}$. Spectra of SN2010jp display an unprecedented triple-peaked
H$\alpha$ line profile, showing: (1) a narrow (800 km/s) central component that
suggests shock interaction with dense CSM; (2) high-velocity blue and red
emission features centered at -12600 and +15400 km/s; and (3) broad wings
extending from -22000 to +25000 km/s. These features persist during 100 days
after explosion. We propose that this line profile indicates a bipolar
jet-driven explosion, with the central component produced by normal SN ejecta
and CSM interaction at mid latitudes, while the high-velocity bumps and broad
line wings arise in a nonrelativistic bipolar jet. Two variations of the jet
interpretation seem plausible: (1) A fast jet mixes 56Ni to high velocities in
polar zones of the H-rich envelope, or (2) the reverse shock in the jet
produces blue and red bumps in Balmer lines when a jet interacts with dense
CSM. Jet-driven SNeII are predicted for collapsars resulting from a wide range
of initial masses above 25 $M_{\odot}$ at sub-solar metallicity. This seems
consistent with the SN host environment, which is either an extremely
low-luminosity dwarf galaxy or very remote parts of an interacting pair of
star-forming galaxies. It also seems consistent with the low 56Ni mass that may
accompany black hole formation. We speculate that the jet survives to produce
observable signatures because the star's H envelope was mostly stripped away by
previous eruptive mass loss.
