The NFL has been transformed by the mobile quarterback.

That's true of Lamar Jackson and Patrick Mahomes, who combine passing accuracy and quick feet.

That's also true of Tom Brady, who can't outrun a Roomba.

The NFL season began on Thursday night with Mahomes dueling with another exceptional young quarterback, Deshaun Watson.

The Sunday afternoon schedule will highlight a different kind of movement. Brady will start for Tampa Bay, for the first time playing a game for a team other than the Patriots, highlighting a rare season in which a handful of accomplished passers coming off productive seasons have changed teams.

Brady left New England, replacing the productive but erratic Jameis Winston. Teddy Bridge­water, after rehabilitating his knee as backup in New Orleans, replaced Cam Newton in Carolina.

Newton replaced Brady as the starter in New England. Philip Rivers left San Diego and will start for Indianapolis.

Old quarterbacks changing teams isn't new. What's intriguing about this offseason was that each of the veterans who became starters for new teams could, with health and luck, affect the balance of power in the NFL.

This isn't Johnny Unitas wearing lightning bolts; this is more like Joe Montana moving to Kansas City or Brett Favre temping with the Vikings.

Brady's departure could elevate Tampa Bay into a title contender. Newton's mutual-admiration alliance with coach Bill Belichick could allow the Patriots to make the playoffs without Brady. And we might finally get an answer to the seemingly eternal question: Is Brady or Belichick more integral to the Patriots' dynasty?

Bridgewater was a winning quarterback in Minnesota who would have beaten the Seahawks in his first playoff game if not for Wide Left, and who had convinced team leadership that he was poised to lead the team to great heights before suffering a catastrophic knee injury in August 2016. Newton is one of the great dual-threat quarterbacks in league history, and will challenge Belichick to devise an offense that highlights his skills and keeps him healthy. Rivers remains wildly productive yet erratic.

This group of quarterbacks highlights the NFL's great divide. Some teams are scrambling to immediately upgrade the position; others chose a quarterback early in the draft and made him a starter within two seasons of his arrival. The latter group has made the most important position in American team sports also the most fascinating.

Quarterback play has never been better in the NFL, for a number of good and heartening reasons.

Before we get to trends and statistics, let me offer an image, that of Billy Kilmer in 1972. He quarterbacked Washington to the Super Bowl, losing to undefeated Miami. Kilmer was considered an inspirational leader and a folk hero. He also threw a pass that could be described as a wounded duck if you don't mind angering PETA by insulting wounded ducks.

Where would Kilmer fit into the modern NFL? As a backup you never wanted to see play. He'd be the Sean Mannion of Nathan Petermans.

The biggest difference between college football and the NFL used to be offensive creativity. Most NFL teams ran so-called "pro set" offenses. Using a second tight end was considered the height of creativity. Colleges would adapt their offenses to the best quarterback and skill-position players they could find, even if the best quarterback was a pure runner.

The NFL belatedly adapted, and now many of the game's best quarterbacks are accurate passers who can run.

There is no perfect statistic to measure quarterback play, but ESPN's QBR (quarterback rating) is an attempt at a comprehensive evaluation. Last year, four of the first five QBs in the rating were Black quarterbacks with excellent mobility who, 20 or 30 years ago, might not have been drafted as quarterbacks, if at all. The top seven: Jackson, Mahomes, Drew Brees, Dak Prescott, Russell Wilson, Matthew Stafford and Watson.

Sunday, Vikings will start Kirk Cousins. The rising tide of talent at the position means that this season the Vikings will pay Cousins about $40 million to not be a top-10 quarterback.

Jim Souhan's podcast can be heard at TalkNorth.com. On Twitter: @SouhanStrib. jsouhan@startribune.com