MIAMI GARDENS, Fla. (AP) — Joe Flacco was at home a month ago, all but ready to accept his 15-year NFL career might be over.

Then came a phone call from his agent with an invitation to a workout with the Cleveland Browns. A commercial flight and practice squad deal later, the Super Bowl 47 MVP has become an instant star for a team ravaged by injuries but still maintaining playoff hopes.

It can happen almost overnight: a backup quarterback goes from holding a clipboard — or in Flacco’s case, watching at home — to being thrust into action, sometimes at the most important point of the NFL season. They’re on display all around the NFL right now after a flurry of starters have gone down for the season with injuries and teams have needed help to stay in contention.

“It’s one of the more important positions on your team,” said Miami Dolphins coach Mike McDaniel, who called on backups in several games last season, including in the postseason, when starter Tua Tagovailoa missed time with concussions.

“Not only are you supporting the process of the starter, but you have to, at a moment’s notice, go and orchestrate full-speed everything you have worked on. ... It is challenging, challenging, challenging because you never know what’s going to happen.”

Despite the NFL’s efforts to protect quarterbacks, passers are still getting injured in an era in which they are leaving the pocket more and defensive rushers are quicker and more skilled than ever.

At the end of Week 15, 18 teams had started quarterbacks who weren’t their first-string passers on opening day; 56 different quarterbacks have started an NFL game this season. And the list of starters who are out for the season is star-studded: Aaron Rodgers (torn Achilles tendon); Deshaun Watson (shoulder surgery), Joe Burrow (wrist); Anthony Richardson (shoulder surgery); Justin Herbert (broken index finger); Daniel Jones (torn ACL); Kirk Cousins (torn Achilles tendon).

In Indianapolis, Gardner Minshew is 6-4 as a starter this season and has kept the Colts in contention for the AFC South title after the rookie Richardson had season-ending surgery on his throwing shoulder in October. Jake Browning is 3-1 in Cincinnati since Burrow suffered a torn ligament in his right wrist last month. The New York Giants entered Week 15 on a three-game winning streak thanks to the unexpected emergence of undrafted rookie Tommy DeVito.

“When you see guys go out and play well in those situations, it’s pretty impressive because all week they didn’t get a rep,” said Dallas backup Cooper Rush, who is 5-1 filling in for Dak Prescott.

“When you get a full week to prep and game plan and talk with the coach and run the play with the players you’re used to playing with, that helps a lot during the week.”