This is an example of protest. This is specifically against questionable police killings. http://time.com/5322619/antwon-rose-pittsburgh-protest/

The first amendment: "Congress  shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press, or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."