How To Build Database To Support User-specified Attributes?

I have a database that tracks players for children's sports clubs. I have
included representative DDL for this database at the end of this post.

A single instance of this database supports multiple clubs. I would like to
add support for letting each club define and store custom information about
their players. Basically, allows the clubs to define custom attributes for
players (e.g. "height", "weight", "favourite sweet").

A few constraints:
1. Any attributes defined is "private" to the defining club. Other clubs
aren't aware of it although they may define custom attributes of their own
with the same name and type. [Perhaps there is a way to share definitions of
identical attributes?]
2. A club doesn't have to define any custom attributes.

Has anyone done anything similar?. Any ideas on how it might be done?

Kunle


=================== BEGIN DDL ===================
CREATE TABLE FootballClub (
Club_ID int IDENTITY,
Name char(80) NOT NULL,
Area char(4) NOT NULL,
League char(4) NOT NULL,
City char(30) NOT NULL,
PRIMARY KEY (Club_ID)
)
go

exec sp_primarykey FootballClub,
Club_ID
go

CREATE TABLE Player (
Player_ID int IDENTITY,
First_Name char(30) NOT NULL,
Initials char(30) NULL,
Last_Name char(30) NOT NULL,
Date_Of_Birth datetime NOT NULL,
Position char(4) NULL,
Club_ID int NULL,
PRIMARY KEY (Player_ID),
FOREIGN KEY (Club_ID)
REFERENCES FootballClub
)
go

exec sp_primarykey Player,
Player_ID
go

CREATE TABLE UserAccount (
User_ID int IDENTITY,
Club_ID int NOT NULL,
FullName char(80) NOT NULL,
Logon char(20) NOT NULL,
PWD_Hash char(60) NOT NULL,
PRIMARY KEY (User_ID, Club_ID),
FOREIGN KEY (Club_ID)
REFERENCES FootballClub
)
go

exec sp_primarykey UserAccount,
User_ID,
Club_ID
go

exec sp_foreignkey Player, FootballClub,
Club_ID
go

exec sp_foreignkey UserAccount, FootballClub,
Club_ID
go
=================== END DDL ===================