With record field goal, Eagles kicker scores triumph in football - and science

Jake Elliott's right foot slammed into the football Sunday afternoon with more than a half-ton of force, winning the Eagles' home opener with a team-record 61-yard field goal.

While the length of Elliott's kick was impressive, the accuracy was even more so, said University of Nebraska physics professor Timothy Gay, author of The Physics of Football.

After all, elite kickers routinely drive the ball farther than that on a kickoff. But try getting it through the uprights.

The goalposts are only 18 feet, 6 inches, apart, so from 61 yards away, the kicker stood at the narrow end of an extremely long, skinny triangle. His task: keep the football within an angle of less than 5.8 degrees.

For the initial five yards of the ball's trajectory, Elliott had to kick it through an opening just over 18 inches wide.

"The issue is not how far they can kick it," Gay said. "The issue is the distribution of angles."

The record for the longest field goal in the NFL is held by Matt Prater, who kicked a 64-yarder for the Denver Broncos in 2013.

Accuracy drops sharply with field-goal attempts of longer than 50 yards. In 2016, NFL kickers converted just 84 of 146 attempts from 50 to 59 yards, according to pro-football-reference.com — an accuracy rate of 57.5 percent.

And kickers made just one out of four field-goal attempts of 60 yards or longer that year.

Analyzing the physics and biomechanics of kicking a football is a complex problem, in part because of the ball's oblong shape. When punting, the kicker starts with the ball in his hands and is able to impart a tight spiral to improve its aerodynamics. But for a kickoff or field goal, the ball must be kicked from the ground, and it spins end over end during flight.

Chase Pfeifer knows the problem from both ends. He was a backup kicker at Florida State University in 2006 and 2007, and later wrote a 133-page thesis on the topic for his Ph.D. in biomedical engineering at the University of Nebraska.

Pfeifer studied four collegiate place-kickers in a laboratory setting, and he also measured the trajectory of a football on a mechanical kicking machine. Coming off the foot of the human kickers, the ball traveled with an initial velocity of about 65 mph.

The key muscle groups involved in generating that kind of speed were the core, the thigh, the shank, and the foot, said Pfeifer, who is now head of the rehab engineering program at Madonna Rehabilitation Hospitals in Lincoln, Neb. But the key to good kicking is not raw muscle mass, he said.

"The timing of muscle activation was actually more important than muscle strength in achieving that higher foot velocity," Pfeifer said.

In Gay's book, the physicist calculated the force that an elite kicker's foot exerts on the ball during the eight milliseconds of contact: an average of about 450 pounds, with a maximum force of more than 1,000 pounds.

The Eagles' Elliott got a boost on Sunday afternoon from the higher temperatures, as hot air is less dense, allowing the ball to travel farther. But he also was faced with a slight side wind, which apparently affected an earlier attempt — a 52-yarder that missed to the left side.

"It started down the middle, and it kind of ended up fading left with the wind there," the kicker recalled. "I wasn't completely demoralized by it, but I definitely wanted another shot there."

With just a few seconds remaining in the game, he got one. And he made it count.