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The Seattle Seahawks' preseason opener against the Denver Broncos devolved into a game of flag football, which wasn't unexpected in light of the NFL's renewed emphasis on illegal contact and holding.

Surprisingly, only a handful of the 25 penalties called in Denver's 21-16 win Thursday night fell into those categories — and all of those were whistled on the Broncos.

Many believe the NFL's crackdown is in direct response to the Seahawks' "Legion of Boom" defense and the Super Bowl champs' habit of pushing, pulling, tugging and shoving wide receivers.

Most were for old-fashioned transgressions, some stemming from the bad blood that developed between the teams in the wake of Seattle's 43-8 shellacking of the Broncos in the Super Bowl.

"There was one hands-to-the-face penalty, which is a new emphasis. There were no offensive PI (pass interference) penalties called, which is a new emphasis," Seahawks coach Pete Carroll said. "It was just on our end of it, just pretty sloppy play."

There were only eight flags thrown in the Hall of Fame game between the Giants and Bills that kicked off the preseason. Aside from Seattle-Denver, there were five other games Thursday night and they featured an average of 12.8 flags, half of what was walked off at Sports Authority Field, where there was one moan-inducing stretch of penalties on five consecutive snaps.

"To be honest with you I think the referees did a really good job on both sides," Seattle quarterback Russell Wilson said. "We got some penalties on us defensively and offensively, they got some penalties on them defensively and offensively. I think the referees are doing a great job trying to keep it as clean as possible. This game is tough as it gets already, and so I think the referees did a tremendous job tonight."

All those yellow flags littering the field, however, bogged down the game that also had a 46-minute lightning delay in the first quarter.

"It was just out of rhythm, a real sloppy, choppy game," Seahawks safety Earl Thomas said.

Denver had a dozen penalties for 95 yards.

"We knew there was going to be a lot of flags," Denver defensive tackle Terrance Knighton said. "It's the preseason, and it's a lot of new rules — you can't touch receivers any more than you already couldn't, whatever that means. But it's just things we can improve, we'll improve, but physical things, that's football."

Seattle's 13 infractions for 131 yards included: unnecessary roughness, taunting and unsportsmanlike conduct to go with three neutral zone penalties, an offside call, a chop block, a pass interference, encroachment, offensive holding on a lineman and two false starts.

Seahawks star cornerback Richard Sherman said recently that the league's re-emphasis on illegal contact and defensive holding "will have very minimal impact on our game and how we play it."

Broncos star receiver Demaryius Thomas, who was Denver's lone bright spot in the Super Bowl with a record 13 receptions, said he didn't notice any difference in the Seahawks' physical pass-coverage style.

"Like they did in the Super Bowl, they got in our face, pressed, and we were able to go out and convert," said Thomas, who had five catches for 52 yards Thursday night.

The last time the league made illegal contact and defensive holding a point of emphasis was in 2004 amid complaints that New England's defensive backs were mauling Peyton Manning's receivers.

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