[SRW]

Seattle Rules:
C: Depends on where it lands.

If the trespassing ball lands on the field where it's in the "area of the action" then kill the play, reset runners/batter/pitchcount to the beginning of the play. (Yes, a do-over)

If the trespassing ball lands on the field where it's not in the "area of the action" (i.e. ground ball to F5, and the trespassing ball lands in right field) then play on, then kill the play at the end.

Purely judgement.

We don't have this happen too often in our JO FP Tourneys, since we have a multi-thousand dollar netting system inbetween the fields. But some complexes we use that don't have nets, so the above is typically how we inform the umpire crew to work.