Fraud is indirect physical force because the defrauder forcibly holds on to some value of yours and/or withholds some value owed to you. Embezzlement is a straightforward example of fraud and of indirect physical force. The embezzler physically takes wealth that doesn’t belong to him, withholding it from its rightful owner.
In his Advanced Seminars on Objectivism, Peikoff answers a question about libel (just after the 1-hour mark in lecture 14 on Government). He says that for libel to be a rights violation, it has to demonstrably deprive a person of property (like if someone libels Rand and then book sales immediately drop). I’ve heard some Objectivists make another argument: Libel deprives a person of his property in the form of the reputation he has earned. This, though, seems like a very hard case to make, because you cannot objectively prove that others have lowered their opinions of a person on account of someone’s libel—and if those people lower their opinions on the basis of non-objective charges, then what is their opinion actually worth?