answer. There is no "massive" income tax break for NFL owners - that's another of Trump's "alternative facts".
All income from NFL revenue streams is subject to tax (under current law). What tax breaks is your president referring to? My initial response was that trump is naive in this area - he has no freaking clue what he's talking about. Trump could attempt to set up a "double taxation" on NFL revenue - but the owners' attorneys & accountants are smart enough to get around that.
Here:
https://sports.yahoo.com/trump-attacks-nfls-massive-tax-breaks-twitter-130318649.html