The Physics Of A Football Player's Performance

The New York Giants' Brandon Jacobs is a 6'4", 270 pound running back. And with that kind of size, you think he'd be able to run right through would-be tacklers, especially when he only needs to pick up a few yards. But he often can't — Jacobs's stats are below average in those situations. A couple NFL greats and a physics professor have the answer.

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And I'm Melissa Block. We're going to spend the next few minutes on this weekend's big game: the Super Bowl between the New York Giants and New England Patriots.

Quarterbacks Eli Manning and Tom Brady will no doubt be key to their team's success or failure, but in the case of the Giants, so will running back Brandon Jacobs. He presents something of a puzzle in pro football. Jacobs is large for his position. In fact, he's the largest running back in the NFL, but when his team needs just a yard or so for a first down and the chance to keep moving down field, he often falls short.

Here's NPR's Mike Pesca with a lesson in football physics.

MIKE PESCA, BYLINE: Brandon Jacobs is a big back. Look at him. He dwarfs linebackers. Read that stat sheet: 6'4", 264 pounds. Forget the stat sheet. Check out his license plate. Big back. The New Jersey Department of Motor Vehicles doesn't issue that to just anyone. Right?

So you'd expect such a big back to be able to pick up a single yard pretty easily, but according to the website Football Outsiders, over the last three years, Jacobs has failed almost half the time in third and one and fourth and one situations.

The league-wide success rate in those situations is 63 percent. Among NFL defenses, there is a book on Brandon.

DERRICK BROOKS: Don't let him get going.

PESCA: That's nine time all-pro linebacker Derrick Brooks, who, as a member of the Buccaneers, faced Jacobs. Here's a page from the old playbook.

BROOKS: And we all like to say, hit him before he gets going. Somebody get penetration to make him go lateral. Don't give him a downhill vision because he gets downhill vision, then all that 270 of his is coming downhill.

PESCA: Brooks says Jacobs needs to run behind his pads, meaning charging into the hole with head up and shoulders low, deny defenders a clear shot.

Solomon Wilcots was a hard tackling safety for three different teams in his NFL career. He talks about the process of bringing down such a big back.

SOLOMON WILCOTS: You never tackle a man where his strength lies. It's like knifing through a board. If you're a taekwondo, you don't hit the board. You got to knife and make impact through the board to get it to break and that's how you take down big guys.

PESCA: What Wilcots and Brooks are describing in their vernacular is actually a constant of the physical universe. Timothy Gay, a professor at the University of Nebraska and the author of "The Physics of Football," says Jacobs has Newton's first law on his side once he's in the open field, but to get into the open field can be a problem.

TIMOTHY GAY: He's tall. He's got a lot of mass. The reason mass is bad in a running back is that it's hard to make a cut. To juke a guy, you've got to accelerate that mass, which requires a large amount of force.

PESCA: I wrote F=MA on a notepad. I then queried former NFL defensive player of the year Brooks on physics.

You know that formula. Right?

BROOKS: What's that?

PESCA: Force equals mass times acceleration. We're talking about the A. You don't let him get that acceleration because he has that mass.

BROOKS: And a downhill runner with acceleration, I don't care if you're weighing 180 pounds. Man, you a problem.

PESCA: Good defenders know practical physics. Good coaches do, too. It's why the Giants like to toss the ball to Jacobs on sweeps or throw it to him on the run when he's already moving. An object in motion tends to stay in motion until shoved out of bounds. Newton said that - Cam Newton.

Mike Pesca, NPR News, Indianapolis.

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