Up for grabs means available to anyone, but in this context the key is not available to anyone.
Context: "The key will be unclaimed and available to anyone, but he 'll be too weak to make a play for it, leaving the field wide open for you." Claim: "The key will be up for grabs, but he 'll be too weak to make a play for it, leaving the field wide open for you."
Considering the context, is the claim true, false, or unknown?