The first time mechazilla attempts to catch a booster. After the booster has flown defined as having zero contact with the ground or any structures. Will that booster explode. Contact must be made between mechazilla and the booster. If the mechazilla changes name the new name will apply. Explosion must occur within 60 minuits of first contact.
Sep 15, 8:25pm:
Related questions
MOD ACTION -
Extended the close date by a year, as it's unclear when this might happen (and it'd be silly to stop trading)
The booster doesn't bellyflop, so it's able to do a conventional aim-to-miss-the-correct maneuver. This is the same trick Falcon 9 uses to make it so that boosters which fail to land due to engine-out go into the water instead of hitting the barge or landing pad. So any failure prior to landing burn ignition misses Mechazilla and isn't counted. That leaves guidance, last-second engine-out or engine-underperformance, and structural failure of the catch-points as the obvious remaining risks.