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The "tapped" clause is the whole transaction. Unsummon will bounce anything for the same single blue mana; this spell asks for more setup in exchange for the scry, and the price of admission is that the target must already be tapped. That single word reroutes the card from a proactive tempo play into a reactive one. You cannot fire it on an untapped blocker before combat, and you cannot cast it at all when nothing on the board is tapped, because it needs a legal target to go on the stack. The window it lives in is the defensive turn: you let an attacker commit, wait for it to tap to swing, then send it home, undoing the attack and stranding whatever mana or tricks were spent to support it. The scry 1 is the rider that softens an otherwise narrow effect, smoothing your next draw whenever a bounce was already worth casting; it never lets you cast the spell in a vacuum, since the target requirement gates everything. This is the conditional, slower-to-fire end of the long line of blue bounce that runs back through Unsummon and Vapor Snag: same rate, narrower trigger, a small card-selection sweetener bolted on to justify the restriction. The spell earns its mana only against creatures that have already done the thing you wanted to punish.