13 Il. We turn to the question of joinder, which provides a separate and independent ground for reversal. As relevant here, Federal Rule of Civil Procedure 20(a)(2) sets forth that multiple defendants may be joined in one action if the plaintiff seeks relief “with respect to or arising out of the same transaction, occurrence, or series of transactions or occurrences” and “any question of law or fact common to all defendants will arise in the action.” In a multi-Doe copyright infringement lawsuit such as this, at least one issue of law or fact will generally be common to all defendants—here, that issue might be whether AF Holdings has a valid copyright in Popular Demand. But whether all of these Doe defendants could possibly have been a part of the same “transaction, occurrence, or series of transactions or occurrences” so as to support joinder is a more difficult question. If a plaintiff such as AF Holdings can claim no good faith belief that all the Doe defendants are linked in this way, then the logic for denying or at least limiting discovery is the same as that delineated above with respect to personal jurisdiction and venue: information about individuals who could not be joined in an action cannot possibly be “relevant to the subject matter involved in the action.” Fed. R. Civ. P. 26(b)(1). According to AF Does it named in presumptively proper BitTorrent file-sharing to download necessarily transactions. necessary to considering Holdings, joinder of the 1,058 John the underlying suit was at least because, given the properties of the protocol the defendants allegedly used Popular Demand, each defendant was part of the same transaction or series of Some background on the nature of BitTorrent is understand this argument. As Judge Harold Baer, a case very much like this one, explained: