How much of the TV audience do you think the NFL can lose before it begins to damage them financially?
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The NFL is protected some by contracts. ESPN and other broadcasters are on the losing end of the contracts and will feel the effects first.
Only until the contracts are up for renewal. And who knows what legal remedies the losers in this situation might seek if the loss of audience continues. Most of the NFL's and other pro sports organizations' profits, and player's salaries, are tied to the TV audience and to a lesser extend other sources of income.