I'm going to take a very rare exception to Andy's comments. The "exceptions" he suggests are in the Regulation Z citation in my earlier post aren't examples of set off. They are legal actions and court orders. "Set off" means a situation in which "I owe you $X and you owe me $Y. I'm taking as much as I can from what I owe you [$X - $Y] to satisfy your debt to me, and I'd doing it without going to court or relying on anything you signed." Usually, you'd be in default before I would use set off (but sometimes it's a consensual thing between reciprocal obligors: my grandfather used to offset his trade payables against his trade receivables when he was selling heating oil to businesses in our area)
As for the paragraph 3 scenario, it refers to an agreement a cardholder might sign to authorize the card issuer to deduct a monthly payment or account balance from the cardholder's deposit account. The deposit account need not be held by the card issuer. But the agreement would be subject to the cardholder's rights under the Billing Rights provisions in §226.13, and, like any other agreement, could be canceled by the cardholder just by revoking the authorization. As long as the authorization exists, you can continue to pull from the deposit account. But that's not a set off, and presumably, there would not have been a default unless the deposit account cupboard was bare at one time or another.