Eligibility to represent a nation typically derives from legal citizenship, attained either through birth of the participant or a recent ancestor, or through residence, marriage, or other means.
In 2004, FIFA amended its wider policy on international eligibility, ruling that players must be able to demonstrate a "clear connection" to a country that they had not been born in but wished to represent.
[2] The residency requirement for players lacking birth or ancestral connections with a specific country was extended from two to five years in 2008.
In addition to rules related to birth and biological ancestry, World Rugby, the governing body for rugby union, specifies that if a player has been legally adopted under the laws of the relevant country, descent is traced through the adoptive parent(s).
[6] Change of nationality by participants in international sporting events has been the subject of academic study.