Mayor Pete Buttigieg is going to bat for Colin Kaepernick ... telling TMZ Sports he supports the QB's right to take a knee during the national anthem -- and he's ripping Trump for going after the protesters.
"The way I feel about it is the flag that was on my shoulder when I served represented, among other things, our right to free speech," Mayor Pete -- a Navy veteran -- told us in New York.
"You don't have to like it, but one of the reasons we serve was to defend that right, the right of peaceful protest and the idea that we can protest what is wrong with our country.