The Sting and NASL are bad examples to cite, as NASL jerked around with their fields and rules and generally ignored guidelines. FWIW, FIFA regs and the laws of the game do give fields some variance, but in this case it's not the length that would be an issue; it would be the width. A soccer field is usually 110-120 yards long, but international dimensions for width are supposed to be between 70 and 80 yards wide. The minimum width required for a non-international match (which is what this would be) is 50 yards, but that's at minimum. The average EPL field is 114x74. If they tried to use the NW/IL layout as a rough template, it still wouldn't work, because the corner of the pitch that would fall in RF wouldn't give enough room beyond the touchline for corners or throw ins down the right field line. If you tried to shift the layout more towards the center, you end up having to confront the curve of the CF wall. United and the other EPL teams sans Arsenal stress flank play. The point of a summer tour would be to strengthen the brand, maximize revenue and get ready for the season to start. Playing on a 115x50 or so field in a facility with a maximum capacity of slightly over 40,000 is a poor way to do two of those things. If they played here, they'd play in Soldier Field to maximize revenue and actually have a playable field. (FWIW, Soldier Field will likely have some open dates as the CONCACAF Gold Cup-our regions version of the European Championships-didn't select Chicago as either a SF or Final venue.) Finally, United were just here this past summer touring. Barca's going to be here this coming summer. United just signed some deal or another in Asia to market their brand there. I'd bet this is where they end up this coming summer.