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 former Super Bowl MVP has become an overnight hero for a team ravaged by injuries but still trying to maintain 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 year 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 head coach Mike McDaniel, who called on backups in several games last year, 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 of the NFL season, 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 year 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 quarterback 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.”

San Francisco's Brock Purdy went from the final pick in the NFL draft to winning his first seven starts and leading the 49ers to the NFC title game after they lost first and second stringers Trey Lance and Jimmy Garoppolo to season-ending injuries last year. Purdy is 16-3 as a starter and is an MVP candidate this season for the NFC-West leading 49ers with 3,795 yards, 29 touchdowns and a 119.0 passer rating.

Not all teams are as lucky.

The New York Jets entered the season with Super Bowl aspirations after landing Aaron Rodgers in the offseason, but after the former league MVP tore his left Achilles tendon on the fourth snap of his Jets debut, the team's postseason hopes fizzled as they have shuffled struggling backups in and out of their lineup.

But the production of veterans like Flacco, who is 2-1 with the Browns, and young standouts like Purdy shows the value of a solid second stringer. The recent success of backups shows the talent gap between starters and backups may be narrowing, said Pittsburgh Steelers defensive coordinator Teryl Austin.

"When you look at the league in terms of it’s not all five-, seven-step drop back (anymore),” Austin said. "There’s a lot of play action. There’s a lot of different things where you can protect a quarterback. He can be very accurate. He could get the ball out of his hands and that offense can keep moving. So if and when the quarterbacks do get hurt, there’s not a big drop off.”

The Browns have had four different quarterbacks start and win this season and have stayed in playoff contention despite the juggling act. Cleveland has also gotten wins from rookie Dorian Thompson-Robinson and P.J. Walker since Watson's season-ending shoulder surgery.

Cleveland caught some criticism for trading backup Joshua Dobbs before the season, leaving the team vulnerable at the position. Dobbs, who was traded from Arizona to Minnesota in October, has had some solid performances for the Vikings.

“I don’t ever overlook that position and say, ‘OK, we’ve got our starter,'" said Jacksonville Jaguars coach Doug Pederson, who spent most of his 10-year NFL career as a backup. “You can’t. When you do that, it’s going to bite you at some point and you’re not going to have a backup and/or a backup that’s ready.”

Jacksonville signed sixth-year quarterback C.J. Beathard to a two-year extension in February after he spent the past two seasons as Trevor Lawrence's backup.

“Having a veteran like we do and — I would say most teams — that’s pivotal,” Pederson said. "You see it. This is a tough sport. You see how many quarterbacks have gone down or at least out for a period of time. Having a guy that’s been around and played meaningful games in this league helps.”

Most backups get few, if any, reps in their team's system throughout the week. They work mostly with the practice squad helping to mimic the plays and style of an upcoming opponent.

Mike White, Miami's backup and a former Jets backup, stands near Tua Tagovailoa in practice and visualizes the play in his mind as Tagovailoa is getting reps with the starters. When he goes home, White draws out the plays, speaks them into a voice recorder and listens to them in his earphones, pretending that he's receiving the plays through a helmet.

White repeats this routine every week, whether he sees the field on gameday or not. The third-year quarterback hasn't started a game this season, with his only action coming during garbage time for the AFC East-leading Dolphins.

But White said he prepares every week like he's going to be the starter because he knows too well the whirlwind of being thrust into action, having come in mid-game for an injured Zach Wilson his rookie year with the Jets.

“At that point, your heart kind of starts racing,” White said, lightly tapping on his chest to mimic an increased heart rate. “You've got to calm yourself down. It’s hard to just kind of go from just sitting there doing nothing. You’ve got to go out there and try to just operate and trust your preparation. That’s where if you’re not prepared it can come back and bite you.”