A sport is a mutation. Rose plants mutate color sports, climbing sports and dwarf sports.

[From The Practical Book of Outdoor Rose Growing, by George C. Thomas, Jr., p. 25:] Sports are purely a matter of chance, and occur when any given variety shows a bloom or habit of growth different from the accepted plant. [The author cites two well known examples of sports, p. 26:] 'Duchess of Albany' (a sport of 'La France') and 'Ecarlate' (a sport of 'Camoens'). With these two new varieties the habit of growth of the plants remained practically the same as their parent plants; it was only in the color of the rose that the change manifested itself.

[From The Old Rose Informant, by Brent C. Dickerson, p. 70:] the Centifolias... often tend to turn back into the variety which sported them