Adopted by FIFA in 2008, 6+5 rule is designed to counter the Bosman ruling, especially with the increases in the number of foreign players that are under contract by European clubs. The guidelines of this rule mandate that each club requires to field at least six players that are eligible to play for the national team.

In Bosman ruling, the guidelines refer to the transfer players not being allowed to play professional football in the European Union. The 6+5 rule, on the other hand, is mandated to field six players, prohibiting them from playing. For the non-eligible players that are under contract with European clubs, there are no restrictions.
The Objective of the 6+5 Rule
The purpose of adopting the 6+5 rule is to restore the national identity of football clubs. Since most football clubs resorted to allowing foreign players to play on the field, the objective of FIFA is to reduce the gap between big and small football clubs. The name of the rule came from the 11 players of each team at the start of the match. During the game, 6 out of the 11 players are required to play on the field. These six players should be eligible to play for the national team. For the remaining five players, there are no restrictions imposed on them.
What the European Union Thought about the 6+5 Rule
Although FIFA has adopted the 6+5 rule, the European Commission and most European governments deemed the rule illegal. Despite being approved by 155 of the member nations of the organization, the EU government states that the guidelines can lead to discrimination at work. The rule also restricts the players to move freely.
According to the Institute for European Affairs, which is commissioned by FIFA to study the issue surrounding the rule, there is no foul play on the free movement of workers under the laws of the European Union. However, the EU still stands in its decision that the rule could constitute indirect discrimination based on the general interest. Although the privilege of the 6 players to be on the field is not based on the player’s nationality, the European government feels that it considers the entitlement of the player to be part of the national team.