#6 Tape-Trading
Before the Internet became what it has become in recent years, many professional wrestling fans were known as "tape-traders." They collected footage -- on VHS, of course -- and would trade it with other fans, swapping things that could not be easily found or purchased. Supposedly, tape-traders were who helped create all the hype that led to locating the now-found late 1980s match between Bret Hart and Tom Magee - which can now be seen on the WWE Network.
As with other "jam bands," Phish permits attendees to record their live concerts. While the band themselves also sell inexpensive, high-quality recordings and/or streams of its concerts, this fan-friendly approach keeps Phish fans hooked, since no two Phish shows are known to carry an identical setlist. In fact, these live recordings have helped to make recurring traditions like Phish's Halloween shows into legendary and highly-sought-after events.
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Aside from professional wrestling and Phish, I cannot think of many forms of entertainment which attract tape-traders and the like. I do not believe I have ever encountered an NBA or NFL-related collector of that sort, especially since few people re-watch old or "classic" games the way that fans may revisit a notable concert or wrestling event.