Sam Goddard Day (1818 - 1838), usually referred to as Sam Day, Jr., was a British jockey who became the youngest winner of the St Leger when he won on Mango in 1837.Day was the second son of John Barham Day, of the famous Day family of horsemen. Although he was round-shouldered, he achieved his success by being exceptionally strong and keeping his cool.His victory in the St Leger was a lucky one.