  At an age of 4 Gyr, typical solar-type stars in M67 have rotation rates of
20-30 days. Using K2 Campaign 5 and 16 light curves and the spectral archive of
the WIYN Open Cluster Study, we identify eleven three-dimensional kinematic
members of M67 with anomalously fast rotation periods of 2-8 days, implying
ages of less than 1 Gyr. We hypothesize that these anomalously fast rotators
have been spun up by mass transfer, mergers, or stellar collisions during
dynamical encounters within the last Gyr, and thus represent lower-luminosity
counterparts to the blue straggler stars. These 11 candidate post-interaction
stellar systems have much in common with the blue stragglers including a high
binary fraction (73%), a number of long-period, low-eccentricity binary
systems, and in at least one case a UV excess consistent with the presence of a
hot white dwarf companion. The identification of these 11 systems provides the
first picture of the low-luminosity end of the blue straggler distribution,
providing new constraints for detailed binary evolution models and cluster
population studies. This result also clearly demonstrates the need to properly
account for the impact of binaries on stellar evolution, as significant numbers
of post-interaction binaries likely exist on cluster main sequences and in the
field. These stars are not always easy to identify, but make up ~10% of the
spectroscopic binary population among the solar-type stars in M67.
