  ANITA's fourth long-duration balloon flight in late 2016 detected 29
cosmic-ray (CR)-like events on a background of $0.37^{+0.27}_{-0.17}$
anthropogenic events. CRs are mainly seen in reflection off the Antarctic ice
sheets, creating a characteristic phase-inverted waveform polarity. However,
four of the below-horizon CR-like events show anomalous non-inverted polarity,
a $p = 5.3 \times 10^{-4}$ chance if due to background. All anomalous events
are from locations near the horizon; ANITA-IV observed no steeply-upcoming
anomalous events similar to the two such events seen in prior flights.
