Resolves positively if the military of any other country than Ukraine, in order to provide air defence for Ukraine, shoots down or damages at least one drone, missile or aircraft that belongs to Russia or Russia's allies and is in Ukrainian airspace or headed there. The units providing the air defense may be inside or outside of Ukraine.

The action has to happen under a deliberate policy of providing some air defence coverage for Ukraine. An unexplained one-off incident or some unit acting in self defence against a perceived threat to themselves outside Ukraine does not count. I assume such a policy is publicly announced but a non-announced policy also applies if it is obviously in place.

The question is motivated by the discussion of Poland or other NATO countries providing air defence for western Ukraine from their own territory, but I included other scenarios that fit the above criteria.

I think the criteria are objective enough, so I may bet myself.