Detroit
Detroit is one of 12 American metropolitan areas that are home to professional teams representing the four major sports in North America. All these teams but one play within the city of Detroit itself (the NBA's Detroit Pistons play in suburban Auburn Hills at The Palace of Auburn Hills). There are three active major sports venues within the city: Comerica Park (home of the Major League Baseball team Detroit Tigers), Ford Field (home of the NFL's Detroit Lions), and Joe Louis Arena (home of the NHL's Detroit Red Wings). A 1996 marketing campaign promoted the nickname "Hockeytown".

Q: How many metropolitan areas boast teams from all major US sports?
12