If Yone Blademaster moves to Reavers Row and the opponent has one unit there, does Yone's ability trigger to kill the unit if the opponent moves their unit back to base from Reavers Row?

Ruling: No, Yone's ability does not trigger. The battlefield was never "open" because the opponent had a unit there when Yone arrived, so conquering it through combat does not count as conquering an open battlefield.

Nuances:

• The term "open battlefield" is not currently defined in the CRD, which could potentially affect this ruling if a definition is added later
• A combat showdown does occur because units were present when combat started, but this doesn't make Yone's ability trigger
• Conquering a battlefield in combat is not the same as conquering an "open" battlefield