This isn’t new. In the NHL both the Blues and the Predators began making efforts earlier this year to keep Blackhawk fans away. Watching the games on TV they don’t appear to have been successful.
Watch a Red Sox/Rays or Yankees/Rays game at Tropicana Field. It is always more fans supporting the visiting team than the Rays. This is especially true in September if the Sox or Yankees are competing for the AL East and the Rays are out of it.
Camden Yards actually raises the price for Red Sox games because of the Southwest $49 one way fares out of Manchester, Providence and Boston to Baltimore. People fly to Baltimore, watch the weekend series and the fly home on Sunday afternoon. You can still buy a $20 ticket in the upper deck. This year will be another season where Sox tickets at Fenway will be impossible to get.