A corruption of Ricards, from Richard (which see).

Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.

RICKETTS. " I will, while 'tis in my mind, insert this remarque; viz., about 1620, one Ricketts of Newbury, perhaps corruptly from Ricqrds, a practitioner in physick, was excellent at the curing of children with swoln heads and small legges ; and the disease being new, and without a name, he being so famous for the cure of it, they called the disease tlie ricketts ; as the King's evill from the King's curing of it with his touch; and now 'tis good sport to see how they vex their lexicons, and fetch it from the Greek P«x'e, the back-bone." Aubrey's Nat. Hist, of Wilts, 4to., p. 74. Dr. Johnson says the uame was given by Dr. Glisson on the first appearance of the disease. Dr. Glisson was contemporary with, and probably known to, Mr. Ricketts, and therefore Aubrey's statement may be correct. He is most likely right, too, as to Ricketts being a corruption of Rickards, which, in its turn, is a corruption of Richards.

Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.