History of retired numbers dates back to Lou Gehrig Day
Bill Russell's No. 6 jersey to be retired throughout NBA
Hank Aaron, Biography, Baseball, & Facts
Yankees Retired Numbers
When every baseball team will run out of uniform numbers - All My Sports Teams Suck
Top 100 MLB players of all time - Nos. 25-1 - ESPN
Retired shirt numbers: Clubs and players to give & receive honour
New York Yankees retired Paul O'Neill's No. 21 jersey
List of National Basketball Association retired numbers - Wikipedia
How many teams in the NBA have retired number 23?
Retired Uniform Numbers in the American League
Jude Bellingham: Birmingham City Retire Number 22 Shirt After Transfer