"riot resulting from racial hostility," by 1875, American English, from race (n.2) + riot (n.). The thing itself is older; in the Jacksonian era it was comprised in the general term mobbing.
Entries linking to race-riot
race n.2
[people of common descent] 1560s, "people descended from a common ancestor, of persons allied by common ancestry," from French race, earlier razza "race, breed, lineage, family" (16c.), possibly from Italian razza, which is of unknown origin (cognate with Spanish raza, Portuguese raça). Etymologists say it has no connection with Latin radix "root," though they admit this might have influenced the "tribe, nation" sense, and race was a 15c. form of radix in Middle English (via Old French räiz, räis). Klein suggests the words derive from Arabic ra's "head, beginning, origin" (compare Hebrew rosh).
Original senses in English included "wines with characteristic flavor" (1520), "group of people with common occupation" (c. 1500), and "generation" (1540s). The meaning developed via the sense of "tribe, nation, or people regarded as of common stock" to "an ethnical stock, one of the great divisions of mankind having in common certain physical peculiarities" by 1774 (though as OED points out, even among anthropologists there never has been an accepted classification of these). In 19c. also "a group regarded as forming a distinctive ethnic stock" (German, Greeks, etc.).
Just being a Negro doesn't qualify you to understand the race situation any more than being sick makes you an expert on medicine. [Dick Gregory, 1964]
In mid-20c. U.S. music catalogues, it means "Negro." Old English þeode meant both "race, folk, nation" and "language;" as a verb, geþeodan meant "to unite, to join." Race-consciousness "social consciousness," whether in reference to the human race or one of the larger ethnic divisions, is attested by 1873; race-relations by 1897. Race theory "assertion that some racial groups are endowed with qualities deemed superior" is by 1894.
riot n.
c. 1200, "the following of a wrong scent by hounds" (a sense now obsolete but in one phrase); early 14c., "debauchery, extravagance, wanton living," from Anglo-French rioute, Old French riot, riote (12c.) "dispute, quarrel, (tedious) talk, chattering, argument, domestic strife," also a euphemism for "sexual intercourse," of uncertain origin. Compare Italian riotta (Medieval Latin riota) "quarrel, dispute, uproar, riot." Perhaps from Latin rugire "to roar."
The meaning "civil disorder, violent disturbance of the peace, public disturbance arising from wanton and disorderly conduct" is attested by late 14c. The meaning "something spectacularly successful" first recorded 1909 in theater slang. The sense of "vivid display of colors" is by 1891.
To run riot "act or move without control or restraint" is by 1520s, a figurative extension of the oldest Middle English meaning of the word, in reference to hounds following the wrong scent. The Riot Act, part of which must be read to a mob before active measures can be taken, was passed 1714 (1 Geo. I, st.2, c.5). Riot girl and alternative form riot grrl first recorded 1992.