Sorry, this makes no sense. Economic impact is measured in revenue to local businesses. Unless the NFL/team owns all of the local retail, restaurants, tolls, parking lots, tourism and associated taxes, there is no way the NFL/team could ever realize that revenue. We can debate the actual revenue impact (check out the "profitability" of the Olympics: http://www.npr.org/blogs/money/2012/07/23/157224211/olympic-...), but the standard you propose is incorrect.

The economic impact of a stadium or other large public works project is based in calculators that are usually published by the state economic development agency. It's more of an art than a science, and like any projection made over a period of 30 years, they rarely hit their numbers.

Public financing of something like a stadium or arena does three things: eliminates a tax liability for the teams/other users, eliminates risk, as the local taxing authority ultimately owns the debt, and keeps the labor and trade unions happy, and stadium projects keep the guys on the payroll.

Ultimately, all of people in a taxing district bear the burden of these giveaways. If I could apply for a full property tax exemption in NY, the $6,000/year I pay for my modest home would be used for capital improvements like a kitchen, solar panels and siding. That would give some construction dudes jobs, and generate more value. The government easily spent $100m on Super Bowl security. That's a lot of money spent better elsewhere or not at all.

That, or they also know that they can offload the cost onto the cities whose governments are willing to pay for it, instead. In such cases, why would the teams spend the money themselves?

This is really insightful. Why didn't I think of this?