So do the Marine Corps. There's no way to protect every high school or small college stadium, but it's entirely possible to deploy 50+ Stinger units around the country every weekend.

The FAA is already enacting TFRs (Temporary Flight Restrictions) around major sporting events every week, so part of the plan is already in effect. For really major events like the World Series, it might be necessary to expand the TFR boundaries and to maintain a Combat Air Patrol over the city. I really hate thinking about things like this but we have to accept the reality of terrorism in America. It'll likely be a long time, if ever, before life fully returns to normal.

Most major sports statiums are located in big cities that have Class B airspace. Since the Sept 11th attacks, Class B airspace has been expanded and no VFR (visual flight rules) flights have been permitted. Hundreds of smaller airports that were outside of Class B airspace now find themselves in the "Enhanced Class B" restricted zone where VFR flights are prohibited. This has effectively trapped 41,000 private planes around the country and is having a terrible impact on hundreds of general aviation businesses.

For example, look at this aeronautical chart of the Washington DC area. There are about 20 small to medium sized airports inside that 25 mile diameter red circle where flights are prohibited. The FAA just reduced that to 18 miles, so that will free up some of the airports and trapped planes.