Whenever people speak about college football quarterbacks with mobility nowadays, they're not talking about the guys who can scramble out of the pocket or who can get big yardage out of a run-pass option.

No, in this case it's the ability for quarterbacks to quickly find new homes elsewhere if they don't get what they want at their previous destination. Call it college football's answer to free agency.

Two of the top five teams in the top 25 will be led by transfers: Jalen Hurts at Oklahoma and Justin Fields at Ohio State. And how strange is this? Both quarterbacks came from programs that also are ranked in the top five: Hurts from Alabama, Fields from Georgia.

It's quite a revolving door at Clemson. The Tigers saw two quarterbacks transfer out after Trevor Lawrence committed to the program. Kelly Bryant, who played in four games last season before losing his job to Lawrence, is a graduate transfer starting for Missouri. Hunter Johnson, who left after his freshman season of 2017, is prepared to take the controls at Northwestern.

It was a similar situation at Georgia. The QB line began with Jacob Eason in 2016. After Eason suffered a knee injury in the 2017 season opener, freshman Jake Fromm took over and played the rest of the season, resulting in Eason's transfer to Washington, where he will start Saturday. Fields entered in 2018 and played 12 games but threw only 39 passes, compared to Fromm's 306.

Fields, who first committed to Penn State in high school before reopening his recruitment, entered the transfer portal in mid-December and announced the next month he was heading to Ohio State. He received a waiver in February from the NCAA, meaning he didn't have to sit out a year.

Fields' arrival in Columbus meant the departure of Tate Martell, who packed up for Miami yet could not beat out redshirt freshman Jarren Williams for the quarterback job. He was in on several snaps at wide receiver in the Hurricanes' season-opening loss to Florida.

Give Hurts credit for sticking it out at Alabama for the entire 2018 season after losing his job to Tua Tagovailoa even though he went 26-2 as a two-year starter. At Oklahoma he replaces Heisman Trophy winner and Arizona Cardinals rookie Kyler Murray -- quite a coup for the Sooners.

Austin Kendall, who was supposed to be in the mix to be Murray's replacement before Hurts showed up, moved on to West Virginia as a graduate transfer and will start the Mountaineers' season opener.

Two other top 10 teams are guided by transfer quarterbacks: senior Joe Barrow (from Ohio State) at Louisiana State, and senior Shea Patterson (from Mississippi) at Michigan, though they each have a year of experience in the program.

The transfer bug doesn't affect only ranked teams. Former Penn State quarterback Tommy Stevens left Happy Valley in May for Mississippi State and won the starting job last week. That spurred Keytaon Thompson, the Bulldogs' backup for the last two seasons, to put his name in the NCAA transfer portal one day later.

Of course, all of this movement is possible thanks to the NCAA transfer database, also known as the transfer portal, which was established by the NCAA Division I Council and took effect last October.

The rule states that a student-athlete informs his or her current school of the desire to transfer, and the school has two business days to enter the student's name in the national database. Then coaches of other programs can contact the players without asking his or her previous coach for permission.

James Franklin knows all about the portal. A total of 13 players from last year's Penn State roster transferred to other schools, including nine who moved on as graduate transfers.

"It's an interesting circumstance that we're all in," the Nittany Lions head coach said last month at Big Ten Football Media Days. "But it's where we're at right now. You'd better embrace it. You'd better have a plan and you'd better do everything you possibly can to make sure it's a strength."