The two biggest factors were clearly (1) the giant television contract the league secured with Disney and Turner, and (2) the $2 billion price paid by former Microsoft CEO Steve Ballmer to buy the Los Angeles Clippers.
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The massive step up in value has led to a new wave of interest in selling teams while the market is hot: the Atlanta Hawks and Brooklyn Nets may see sales this year above a billion dollars each. It's hard to imagine another 74 percent jump this year, so owners looking for a quick gain may be smart to get out now. This is one area in which past performance is certainly not indicative of future returns.
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To get some comparison for how great a return the NBA had, consider that only nine individual companies in the S&P 500 saw their stock price increase by over 74 percent. That means the entire NBA—as an industry—had a better return than 98 percent of the stocks in the index. Truly remarkable.