Football is the signature American sport, where grisly men collide on the field and droves of zealous fans flock to the holy shrine of their stadiums.

In East Lansing, Mich., that shrine is Spartan Stadium, in the very heart of Michigan State University's campus.

It's also the center of this environmental inquiry. Saturday game day translates into tens of thousands of people driving, eating, discarding trash, going to the bathroom, firing up grills.

This project takes an essential part of American culture--football--and critiques it with a green eye.

It shows how a football game's environmental impact spans much beyond the campus' borders. The games leave an "environmental footprint" too big to calculate. It's a footprint associated with all activity and one that often goes unnoticed.

"The idea behind the environmental footprint is that the world is a closed system," said Terry Link, chair of MSU's Office of Campus Sustainability. "There is only so much earth and water. We aren't getting more land or water. Since there is a finite amount of stuff and as we use more stuff, we deplete what is available to us. So the footprint charts human consumption and the waste we put back into the environment."

Consider a typical household in Lansing, the community right next to MSU. Assume it is inhabited by three meat-eating people with a car in the driveway that gets 20 miles to the gallon. This modest lifestyle translates into a 17-acre footprint, or the amount of land required to provide the resources for such a lifestyle, according to calculations made by the Earth Day Network in Washington, D.C.

If everyone in the world owned such a home with the same car in the driveway, we would need another 2.9 Earths. You can determine your own environmental footprint here.

Figuring how many earths are needed to support American football would be a complex calculation. But there is no doubt that the sport leaves an environmental footprint beyond campus borders.

"When you look at a football game, there are social benefits, but there are also environmental costs," Link said. "The social benefits are probably wiped out by the environmental damage from the amount of traveling involved with the fans, because some of those fans come from a long way."

Games also produce an alarming amount of refuse, some of which is recyclable. Every game requires a great amount of energy, water, fertilizer to accommodate the tens of thousands of screaming fans.

All of these components complete the puzzle that makes up the footprint. And while these findings will never change the traditions of Spartan football, they may raise eyebrows about the environmental cost of this and other activities that are regularly taken for granted in life's daily routines.

And that's the first step in downsizing the environmental footprint.