a thirty second commercial is about $600K. For some teams, viewership is off 20%. So NFL has to give 20% free commercial time to make up the shortfall in viewership.
Let's say someone bought 10 commercial slots (6 Million). They would now get 2 commercial slots free worth $1.2 million - that's $1.2 million the NFL won't get. Multiply that times 32 markets and 16 weeks, that's a potential loss of $800 million for player salaries next year - TV revenues go almost exclusively toward player salaries.
That could be a lot of pain ...
It's one thing to boycott by not buying from advertisers, buying team gear, or buying tickets to the games. But not watching a game on TV isn't hurting the NFL one bit.