Talk of Colin Kaepernick's decision to sit down during the national anthem reached far beyond football Monday.

And many weren't thrilled with the San Francisco 49ers quarterback's strong words about why he is doing it: to instigate change and challenge authority when it comes to race relations and what he considers police brutality.

Martin Halloran, the San Francisco Police Officers Association president, sent a letter Monday to NFL commissioner Roger Goodell and 49ers CEO Jed York denouncing Kaepernick's "ill-advised" statements and a "naivete" and "total lack of sensitivity" toward police, along with an "incredible lack of knowledge" about officer-involved shootings.

The police union invited Kaepernick or anyone else from the league to visit the San Francisco police academy to build communication and understanding about the profession.

"I only wish Mr. Kaepernick could see the emotional and psychological challenges that our officers face following a fatal encounter," Halloran wrote. "Some are so affected they never return to the streets. In short, Mr. Kaepernick has embarrassed himself, the 49er organization, and the NFL based on a false narrative and misinformation that lacks any factual basis."

Kaepernick, who has sat through the anthem at all three 49ers preseason games so far, is prepared to keep fighting for what he believes in, even alone.

"The fact that it has blown up like this, I think it's a good thing. It brings awareness," Kaepernick said Sunday. "Now, I think people are really talking about it. Having conversations about how to make change. What's really going on in this country. And we can move forward. ...There is police brutality. People of color have been targeted by police. So that's a large part of it and they're government officials. They are put in place by the government. So that's something that this country has to change. There's things we can do to hold them more accountable. Make those standards higher."

Information from The Associated Press was used in this report.