When a creature gains protection from a quality shared by an attached Equipment, the Equipment becomes unattached from that creature immediately as a state-based action. Specifically, CR 704.5n states that if an Equipment is attached to an illegal object, it becomes unattached. Protection prevents a creature from being equipped by sources with the relevant quality (CR 702.16b).
However, becoming unattached simply means the Equipment is no longer attached — it stays on the battlefield as a normal artifact. Equipment have the intrinsic ability to exist on the battlefield independently of any creature. There is no rule that sends an unattached Equipment to the graveyard; only specific card text (like on some Auras) would cause that to happen, and Equipment does not share the Aura rule (CR 301.5, 704.5d applies to Auras, not Equipment).
Auras work differently: if an Aura becomes attached to an illegal permanent, it goes to the graveyard as a state-based action (CR 704.5d). Equipment do not have this same rule and simply float on the battlefield unattached.
Example: Your Maul of the Skyclaves is equipping your White Knight. Your opponent gives the Knight protection from white (e.g., via Standard Bearer's effect). The Maul (a white Equipment) becomes unattached and sits on the battlefield as a 0/0 artifact — it does not go anywhere and can be re-equipped to another creature later.
So to summarize: Equipment that falls off due to protection remains on the battlefield as an unattached artifact, ready to be equipped to another legal creature.
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.