I think Trump said this at that Luther Strange rally, and it really is pretty casual, Trump has his spiel and all he did was say that little bit to a friendly audience and state of the Crimson Tide:
"Aren't you watching football and you see one of these guys kneeling during the national anthem and you wish the coach would just fire that SOB", it is something like this. And the crowd cheered such a statement.
Also, Trump didn't call for a boycott, that's the media or someone putting words in his mouth.
I saw at Drudge; some article and read it, the NFL is not enforcing it's rules to allow this to happen, I heard some others bring up that "peaceful protest" bit as well. I think Michael Jordan might have said this.
Enforce the rules, NFL, this is a disaster,
And Pittsburgh, as mentioned and now with Big Ben coming out, the Steelers in dealing with this situation they did nothing to create got tons and tons of people mad at them, everyone wanted the Bears to beat them yesterday.