Peyton Manning and the Broncos will host the defending champion Ravens on the field where Baltimore knocked Denver out of the playoffs last season. (Jack Dempsey/Associated Press)

After an offseason of playing defense, the NFL returns to action Thursday night, the bright stadium lights in Denver illuminating a sport in the midst of change, both on and off the field.

Little stays the same in today’s league, and oddsmakers have slotted the defending champion Baltimore Ravens as underdogs against the Denver Broncos in the season opener.

While the year-to-year parity and evolving style of play underscore the NFL’s constant state of commotion, the league emerges from an especially tumultuous offseason, one in which the very nature of the game was scrutinized daily.

The NFL is trying to emerge from a dark cloud of player health and safety concerns and last week reached a proposed settlement with about 4,500 former players who were suing over concussions. The league has also instituted new rules this season that will bar runners and tacklers from initiating contact with the crowns of their helmets and has stepped up its efforts to educate youth players on proper techniques. In Baltimore to announce a new initiative related to concussion research along with Under Armour and GE, NFL Commissioner Roger Goodell proclaimed, “There’s never been a better time to play the game of football or be a fan of the game of football. I couldn’t be more optimistic about the future.”

Of the lawsuit settlement, Goodell said, “I don’t know how it’s going to be remembered. I know what its effect is going to be, which is going to provide help for the players and the families that have cognitive issues. . . . Rather than litigating for years, the owners, the NFL and frankly, the plaintiffs, all said let’s go do something that’s great for the game and great for the people and get help to the people that need it. And that’s a good thing.”

Meantime, offseason headlines were dominated by less-than-flattering football news: former Patriots tight end Aaron Hernandez was arrested on murder charges, and armchair orthopedists monitored daily the rehabilitation of Redskins quarterback Robert Griffin III, a rising star who injured himself in the playoffs and needed a total reconstruction of his knee.

On the field, defenses have never been more complex, and offenses never so versatile. Pocket passers such as Matt Ryan, Aaron Rodgers and Tom Brady are still effective, but a new generation of athletic quarterbacks — Griffin, Russell Wilson, Colin Kaepernick — have sent ripples of change across the league. The addition of former Oregon coach Chip Kelly in Philadelphia leaves few doubts: This isn’t your granddaddy’s NFL.

Former coach Jon Gruden says the style of play in 2013 is similar to what fans would see at a college or high school game.

“Players are playing it differently, wide open, no-huddle, spread systems, and that’s what’s in college football. That’s how we’re training coaches and players,” said Gruden, now an analyst for ESPN’s “Monday Night Football.” “It’s a big part of the National Football League.

“I think it’s here to stay. I’m not saying it really excites me as much as maybe it does some other people because I like the conventional way of moving the football, throwing it in a traditional style of offense. But some of these quarterbacks can really make it happen, and it'll be fun to watch.”

The NFL opener will feature two passers from more of a traditional quarterback mold, though Peyton Manning and Joe Flacco are among the game’s best at running a fast-paced no-huddle system. Flacco, the Super Bowl XLVII MVP, is coming off a career year and threw 13 touchdowns and no interceptions in his final six games last season. He may lack the sparkle and pizzazz of the new crop of quarterbacks, but the Ravens rewarded him this offseason with a $120.6 million contract, tying their future to the cannon attached to his right shoulder.

“He can literally do everything,” said Jim Caldwell, the Ravens’ offensive coordinator. “He’s one of those guys who can roll to his left, roll to his right. He’s a very, very fine athlete, and so there are hardly any limits with him.”

The Post Sports Live crew previews the Redskins season opener on Monday Night against the Philadelphia Eagles. (Post Sports Live/The Washington Post)

The Ravens, who’ve won their past five season openers, scored more points (119) and posted more touchdowns (15) than any other team in the preseason. But most analysts have focused more on what they’ve lost from last year’s championship squad: linebacker Ray Lewis (retired), center Matt Birk (retired), safety Ed Reed (Houston) and wide receiver Anquan Boldin (San Francisco) among them.

Baltimore has added defensive ends Chris Canty and Elvis Dumervil via free agency and drafted safety Matt Elam, who is expected to come off the bench Thursday night.

“We all live by that motto around here: ‘In Ozzie we trust,’ ” linebacker Terrell Suggs said of Baltimore General Manager Ozzie Newsome. “In the spring, everybody was hitting the panic button on us because of the guys we lost. Even though we were very sad to see those guys go, the show must go on.”

Across the league, 32 teams have reloaded with new coaches, new players, new goals. In Baltimore, there isn’t much talk about last year’s Super Bowl. While the NFL spent the offseason managing controversy and change, the Ravens were able to bask in their incredible playoff run, from that thrilling double-overtime win at Denver to the three-point nailbiter in the Super Bowl. But that’s over now.

“You start a new year, a new chapter,” Rice said, “and you go through camp, and obviously, when you win a Super Bowl, you can say you feel the pressure. But when you get out of a training camp like we just got out of, and you build the camaraderie that we’ve built, just having Week 1 again is exciting.”