A new season means new signings and new squad numbers. Per the New York Red Bulls' website, the process of allocating numbers to the new members of the team has started. Dan Metzger has been assigned the #6 shirt.
Among the many treasures to be found at MetroFanatic.com is a comprehensive list of every MetroStars and RBNY player by shirt number. From this we learn that Metzger is the 12th player to have worn the #6 for this twice-named club.
The most recent was Anthony Wallace, who spent 2015 with RBNY.