What does Boxing Day have to do with boxing?
late 14c., "body of persons sent on a mission," from Old French legatie "legate's office," from Medieval Latin legatia, from Latin legatus "ambassador, envoy," noun use of past participle of legare "appoint by a last will, send as a legate" (see legate). Sense of "property left by will" appeared in Scottish mid-15c.
in law, generally a gift of property by will or testament. The term is used to denote the disposition of either personal or real property in the event of death.