For UEFA: Squads can be divided into List A and B. List A is the first team, and can contain a maximum of 25 players. Of these 25, eight must be "local" players. What is the break-up for local players?
"Club Trained Players," which refers to a player who was ON THE CLUB'S BOOKS for three seasons between the age of 15 — that is, the start of the season during which he turns 15 — and 21 years old, or the end of the season AFTER he turns 21. There must be FOUR such players. The seasons do not have to be consecutive.
“Association Trained Players,” which refers to a player who was part of another's club's books WITHIN the same Association. That is, the Italian FA; Hence, an Italian Team's Books), for three seasons between ages 15 and 21 again.
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List B can contain an unlimited number of players aged 21 years old or less, who have been eligible to play for THAT club for any uninterrupted period of two seasons between ages 15 and 21 again. That is, these players count outside the 25-man squad, and can be registered freely.