There's no "right" answer. You could say that Astoria lost the Jets to East Rutherford when they moved from Shea to the Meadowlands, that Tempe lost the Cardinals to Glendale when they moved from Sun Devil Stadium to UoP Stadium, that Dallas lost the Cowboys to Irving when they left the Cotton Bowl for Texas Stadium, that D.C. lost the Redskins when they left RFK for FedEx Field in Landover, Maryland. Personally, I wouldn't count those, because the fanbases still kept their teams and the move was a stadium upgrade and not a relocation.Similarly, you could note that places like New Haven, Clemson, Champaign and Memphis had and lost NFL teams, but those were really just pit stops by teams in between stadium projects.Personally, I'd vote for Brooklyn, New York. Dan Topping owned the Brooklyn Dodgers from 1934 to 1943; in 1944 they were renamed the Brooklyn Tigers, and in 1945 they merged with the Boston Yanks as a result of WWII. Brooklyn hasn't had a team since, while every other city that lost a team has since had one put back.Before that, I believe the answer is Portsmouth.