The REG says that interrupt the battle effects interrupt the following abilities if they were activated on cards in the current battle:
1 all active abilities
2 abilities with effects that are defeating one of the characters you control in battle
3 abilities on the last card played in current battle if it was played by your opponent
My question is this: Does a card with abilities satisfying any of the conditions above have to be IN the field of battle when the interrupt the battle effect is played in order to be interrupted? Suppose a character equipped with a weapon that has an ongoing effect (such as a protect effect) enters battle but is then removed from battle; would an interrupt the battle effect played after that character's removal be able to interrupt that ongoing effect?