If Yone moves to a battlefield where Ezreal is defending, and in response to Ezreal's defend ability, Arcane Shift moves Ezreal home, does Yone's battlefield count as an open battlefield?

Ruling: No, it does not count as an open battlefield because the combat showdown had already started when Ezreal used his defender ability, so at the time combat started it was not an open battlefield.

Sequence:

• Yone moves to battlefield where Ezreal is defending
• Ezreal uses defender ability (combat showdown starts)
• Arcane Shift moves Ezreal home in response
• Combat cleanup occurs, but this is not conquering an open battlefield