The Fos Williams Medal has been awarded since 1981 to the best Australian rules football player from South Australia during Inter-State or Inter-Competition matches. The medal is named in honour of legendary South Australian National Football League (SANFL) player and coach Fos Williams.

Originally the award was made in respect of State of Origin matches. Since that competition folded in 1999, the medal has been awarded during games where the SANFL plays other state competitions in State League representative matches (e.g. WAFL v SANFL). The award is usually voted on by a panel selected by the SANFL from significant football identities present at the match, and may include past players, coaches and journalists.

* denotes State League clash, not an AFL-level Origin match
♦ South Australia played no state games in 1990 so the SANFL played a City v Country match at Football Park which was essentially an All-Stars game with teams divided into those recruited from SA's country leagues and those from Adelaide. The concept only lasted one season due to poor attendance.

• Interstate matches in Australian rules football
• Simpson Medal – Western Australia
• E. J. Whitten Medal – Victoria (State of Origin)
• Frank Johnson Medal – Victoria (VFL)

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