I'm not sure if this is in all major cities or just Philadelphia. If you download the McDonalds app, create an account, and log in, whenever the Phillies hit a home run, the next day you will have a coupon in the app fora Free McDouble. I am leaded to believe it's most major cities because the promotion says whenever the home team hits a home run you get a free McDouble.
http://www.mcdonalds.com/us/en/mobile_app.html