The science of slam

Speeds can approach 18 mph. The force can exceed half a ton.

A car crash? No, but it just might feel that way.

It's a football collision. A big one. The kind that can make eyes water and merits a replay or three. A scientist would need precise measurements and some serious calculations to determine the force of a hit. A football player has only seconds, and sometimes not even that long. Certainly not enough time to think about the wicked physics equation that will play out once he puts his shoulder into the 200-pound Super Ball of fast-twitch muscles barreling toward him.

"If you're thinking like that, you're going to get run over," linebacker Lofa Tatupu said.

Better to just grit your teeth, unload your best shot and let the variables sort themselves out.

"When it's two people running full speed, you never know how it's going to happen," linebacker Leroy Hill said. "Hopefully you come out on top and him on bottom. But you never know."

A big hit can change the flow of a game. It energizes the crowd, it intimidates an opponent and it is a real-world manifestation of those science lessons you didn't pay enough attention to.

"It's physics," Hill said.

Mass. Acceleration. Momentum. All coming together in a most primal manner.

"Smashing into someone going the opposite way," Hill said.

Timothy Gay is a Nebraska professor with a doctorate in atomic physics who wrote an entire book on the physics lessons found in football.

In some ways, every NFL game is a three-hour experiment filled with men who are powerful and padded and separated into two distinct groups. The offense is worried about catching the ball, holding onto the ball and forward progress. Defense is more of a bare-knuckles business, men whose primary goal is to render the opponent a twitching pile of laundry. Ask anyone from that half of the football universe to name their biggest hit and get ready to hear some stories.

In college, safety Deon Grant hit a Florida running back so hard he gave himself a black eye. Defensive end Patrick Kerney sent Donovan McNabb flying during a game in 2003 and this year he gave Tampa Bay's Jeff Garcia a shoulder check that nearly buried Garcia in the turf.

Tatupu can't remember the moment he knocked Carolina's Nick Goings out of the NFC Championship Game, but he knows that was his biggest hit, and Julian Peterson once hit Jerome Pathon so hard that Pathon's helmet popped off like a champagne cork.

Safety Brian Russell put quite a lick on Itula Mili, Seattle's former tight end who outweighed Russell by 30 pounds, maybe more. Linebacker Kevin Bentley can recall not only the hit he put on Hines Ward, but the coverage of his Browns defense in that play.

And when everything comes together just right for the defensive player, the result is perfectly devastating. The force of a collision might be distributed equally, but the results are not.

"It's like you hit a sweet spot," defensive end Darryl Tapp said. "You don't feel anything. There really are no words to describe it."

Lesson 1: Objects in motion tend to stay in motion unless acted upon by an outside force. Namely, a carnivorous mouth-breather on defense.

"Most of the time, your big hits, the guy normally doesn't see you," Peterson said. "Either he's cutting away from the next guy or he's looking at something else."

Or he's like Pathon when he played with New Orleans a few years back and Peterson played for the 49ers. Pathon caught a pass, turned upfield and bounced off a couple of 49ers linebackers.

"He got to running up the field thinking he was scot-free," Peterson said. "And I was coming full tilt."

Wham.

Pathon's helmet popped into the air, Pathon went from full speed to flattened in an instant.

"I got up, I was ready to talk," Peterson said. "When I saw that he wasn't coherent ... I felt kind of bad. Like I might have messed him up for the rest of his life or something, but he ended up being OK, so it made me feel a lot better."

The offensive player has one football to hold onto and 11 defenders to avoid. The defensive player has only to worry about: hitting that fellow unfortunate enough to be holding the ball.

Lesson 2: Force = mass x acceleration. The bigger the dude and the faster he can finish the 40, the more likely he is to leave an opponent seeing double.

Kerney's body isn't shaped so much as it is sculpted. Biceps the size of softballs, a stomach that looks paved with cobblestones. But it's his legs that really provide the power. They're the twin pistons that put the Tabasco into a big hit.

"The secret to hitting is hips," said the Seahawks defensive end. "Snapping your hips through."

Kerney sounds almost like a scientist. The professor of punishment who understands that a big hit requires more than just reckless abandon. It takes technique and the knowledge that the less time you're in contact with the opponent, the greater force he will feel.

"It's like the old physics lesson," Kerney said. "So rather than hitting 'em and sort of melting into the guy. Hit him and snap off, that produces a lot more force."

That's how a player laces a hit with gunpowder and why the biggest hits don't always come from the biggest players. In the season-opener this year, Garcia scrambled in the pocket and Kerney decked him with a shoulder check that Garcia didn't see coming until it was too late.

Lesson 3: Momentum is never lost, but sometimes it does get redirected into the cranium of some poor lug.

Tatupu doesn't remember the biggest hit of his career.

He recalls defensive coordinator John Marshall's fevered instructions to get to the edge of Carolina's sweep, which is why he hauled tail to cut off Goings in the first half of the NFC Championship Game in 2006.

But the moment of impact remains a blank spot in Tatupu's memory.

"I don't know," Tatupu said. "I just remember I was on my back looking around."

To give, sometimes you have to receive. The two sides of a collision share the force evenly, which is why Tatupu found himself belly-up at Qwest Field, with his eyes full of stars even though it was the middle of the afternoon.

"I was damned if I was going to stay down," Tatupu said. "Well, he got the best of me, but I'm at least going to get up and play as much more as I can."

Goings left the game with a concussion. Tatupu stayed on the field.

The defensive player feels every bit of the force from a collision as the offensive player. But the defender is usually braced to deliver the blow, and he gets to choose where to hit his opponent. It's the difference between delivering a shot with the shoulder pads and taking one on the chin.

When Bentley was with the Browns, in a game against the Steelers, Ward ran a crossing pattern and Bentley played on the backside. The Pittsburgh quarterback led Ward, who reached out to catch the pass, and Bentley led with his left shoulder and exploded through Ward's body.

Ward got his hands on the ball, but he didn't hold onto it. Not even close. Bentley and Ward hit the turf just like the ball did.

"I got up woozy," Bentley said. "But the fact that I got up and he was kind of stumbling around made it that much better."

It got a little worse when Bentley's teammates arrived.

"Your teammates are slapping you on the helmet," Bentley said. "Oh, great job. Great job. It's like, 'I'm already seeing double, y'all are going to make it worse.' "

Conclusion

Hill needs a minute to decide the biggest hit he's ever put on someone.

Turns out a minute isn't enough time.

"I don't know if I've ever had just a big, big hit," he said.

Oh, he's put some licks on opponents. He knocked Garcia out of Seattle's season opener for a quarter or so and on Sunday in Cleveland he stopped Jamal Lewis cold at the goal line.

But Hill has a specific hit in mind. An ideal, really. Something he looks forward to with the kind of anticipation usually reserved for red meat. It starts with a receiver coming across the middle, his eyes focused on the ball instead of the linebacker who is lining him up like target practice. Then, four steps or so to get to full speed.

"You catch him right up under his chin," Hill said. "Helmet off. Land on the back of his head, feet in the air and you're still standing there.

"That's a big hit."

One that takes place in a fraction of a second. A physicist could spend hours breaking down all the variables. A football player doesn't have the luxury of time or that clinical distance. It's all about immediate instincts and instantaneous aggression, which separates the destroyer from the destroyed.

Danny O'Neil: 206-464-2364 or doneil@seattletimes.com