https://en.wikipedia.org/wiki/Forum_(legal)#Public_forum

The use of public forums generally cannot be restricted based on the content of the speech expressed by the user. Use can be restricted based on content, however, if the restriction passes a strict scrutiny test for a traditional and designated forum or the reasonableness test for a limited forum. Also, public forums can be restricted as to the time, place and manner of speech. In the 1972 case Grayned v. City of Rockford, the Supreme Court found that "The nature of a place, the pattern of its normal activities, dictate the kinds of regulations of time, place, and manner that are reasonable." In determining what is reasonable, the Court stated that "[the] crucial question is whether the manner of expression is basically incompatible with the normal activity of a particular place at a particular time." Thus, protesters have the right to march in support of a cause, but not on a public beach during the middle of the day with bullhorns.