I don't know where the Blitz played (Soldier?) so I can't say for sure, but I never saw them play. Also, I have sadly not had the pleasure of a game at Old Trafford.
Edit: According to wikipedia the Blitz played at Solider Field - but they were an American football team in the USFL. The Chicago Sting were the 70's era soccer team in town and played at Solider, Wrigley, and Comiskey. However that is not what I was looking for either.
So a bunch of teams were guessed for Mo's favorite - out of those teams mentioned I have been to the Chicago Fire's stadium (ok actually three different ones they have used - Soldier, UNI, and Bridgeview) and one other's.
As to why you should believe me? I was wondering why you guys were only pointing at each other. Alas, I am a goodie for true and one of you is the Troll, not sure if the other is the Dragon or a goodie, but we shall see.