The term Cup-tied is used mainly in football to denote a player who is ineligible to feature in a certain knockout competition for having played in that competition for another club that same season.
This rule implies that if a player has featured in a knockout competition for a certain club, then he cannot play in that competition again that season for another club if the latter club signs him. This rule is applied in virtually all domestic and international club competitions, such as the (English) FA Cup, the UEFA Cup and the UEFA Champions League.
This rule is devised to prevent a strong team from gaining what is perceived to be an unfair advantage by signing talented players from clubs that may have been knocked out of the competition in the earlier rounds to make a stronger impact on that competition.