  We identify a new, bright transient in the Kepler/K2 Campaign 11 field. Its
light curve rises over seven magnitudes in a day and then declines three
magnitudes over a month before quickly fading another two magnitudes. The
transient was still detectable at the end of the campaign. The light curve is
consistent with a WZ~Sge type dwarf nova outburst. Early superhumps with a
period of 82 minutes are seen in the first 10 days and suggest that this is the
orbital period of the binary which is typical for the WZ~Sge class. Strong
superhump oscillations develop ten days after peak brightness with periods
ranging between 83 and 84 minutes. At 25 days after the peak brightness a bump
in the light curve appears to signal a subtle rebrightening phase implying that
this was an unusual type-A outburst. This is the only WZ~Sge type system
observed by Kepler/K2 during an outburst. The early rise of this outburst is
well-fit with a broken power law. In first 10 hours the system brightened
linearly and then transitioned to a steep rise with a power law index of 4.8.
Looking at archival Kepler/K2 data and new TESS observations, a linear rise in
the first several hours at the initiation of a superoutburst appears to be
common in SU~UMa stars.
