18 U.S. Code § 2101
https://www.law.cornell.edu/uscode/text/18/2101(a) Whoever travels in interstate or foreign commerce or uses any facility of interstate or foreign commerce, including, but not limited to, the mail, telegraph, telephone, radio, or television, with intent—
(1) to incite a riot; or
(2) to organize, promote, encourage, participate in, or carry on a riot; or
(3) to commit any act of violence in furtherance of a riot; or
(4) to aid or abet any person in inciting or participating in or carrying on a riot or committing any act of violence in furtherance of a riot;
and who either during the course of any such travel or use or thereafter performs or attempts to perform any other overt act for any purpose specified in subparagraph (A), (B), (C), or (D) of this paragraph— [1]
Shall be fined under this title, or imprisoned not more than five years, or both.
18 U.S. Code § 2102
(a) As used in this chapter, the term “riot” means a public disturbance involving (1) an act or acts of violence by one or more persons part of an assemblage of three or more persons, which act or acts shall constitute a clear and present danger of, or shall result in, damage or injury to the property of any other person or to the person of any other individual or (2) a threat or threats of the commission of an act or acts of violence by one or more persons part of an assemblage of three or more persons having, individually or collectively, the ability of immediate execution of such threat or threats, where the performance of the threatened act or acts of violence would constitute a clear and present danger of, or would result in, damage or injury to the property of any other person or to the person of any other individual.