According to online ticket reseller TickPick, sales of tickets for NFL games have declined by 17.9% since Trump challenged the league to crack down on anthem protesters.

Washington Examiner:

From TickPick:

• 17.9 percent decrease in NFL orders this week compared to the previous week.
• Last year the drop was 10.8 percent in orders on Monday & Tuesday following Week Three games.

"We have seen a massive decrease in NFL ticket purchases this past week in comparison to years past. Week 3 seems to usually have less ticket orders than week 2, but this year ticket purchases are down more than 7 percent from this time last year," said TickPick's Jack Slingland.

"While we can't specify if this decrease is due to the president's comments, player and owner protests, play on the field, or simply the continued division of consumer's media attention, the conversation around the NFL this week has focused on the president's comments as well as the players' and owners' reaction. As viewers continue to abandon their NFL Sunday habits, both the number of ticket sales and the purchase price of tickets will drop," he told us.

I would say that cause and effect in this case are particularly clear.  And while revenue from game tickets is only a small part of a team's cash flow, it's a significant indicator of fan discontent and a terrible omen for the future.

The players and owners now say their protest is not against racism or police brutality, but against Donald Trump's remarks.  This is nonsense.  They may sincerely believe they are only pushing back against Trump, but when they take a knee, they are using the exact same method of protest that Colin Kaepernick and the hysterics are using to disrespect the anthem and the flag.

But they can't see that because the cocoon in which they live and work separates them from ordinary Americans from around the country.  The cascade of boos from fans in the stadium who react to players kneeling during the anthem and the threats of a fan boycott are not having much of an effect.  Fewer fannies in the seats – a lot fewer – should get their attention.