For that matter, what, exactly, is a catch? With his team trailing the Green Bay Packers by five points late in the fourth quarter of a divisional playoff game, Cowboys receiver Dez Bryant appeared to have caught a 31-yard Tony Romo pass on fourth-and-2, resulting in a first down at the one-yard line. But Mike McCarthy challenged the catch, leading referee Gene Steratore to review the play and deliver the following lines: "After review, it has been determined that the receiver did not maintain possession of the football during the process of the catch. The ball comes loose, hits the ground. Therefore, the ruling is incomplete forward pass ..." The call reversal changed the complexion of the game, with Dallas going on to lose, and added fuel to an already furious debate over what constitutes a catch in the league.

The Green Bay Packers' collapse against the Seattle Seahawks in the NFC Championship Game left Packers fans with so many "what ifs.
What if Morgan Burnett hadn't slid down after intercepting Russell Wilson?
What if Mike McCarthy's play calling had not been so conservative at the end of the fourth quarter?
What if the Packers had not given up a 69-yard TD drive in a 1:43, which shrank their lead to five points?
What if Brandon Bostick had held on to the ball or allowed Jordy Nelson handle the ball during the onside kick?
What the Packers had stopped Marshawn Lynch from scoring on a 24-yard run?
What if the Packers had sacked Wilson on the 2pt. conversion attempt?
What if Ha Ha Clinton-Dix had knocked down the ball in front of Luke Willson?
What if the Packers hadn't allowed Jermaine Kearse to make a huge catch in OT?
The Packers' inability to close out in crucial situations squashed their dreams of heading to Super Bowl XLIX.

We all now know what PSI stands for.

The biggest football story of 2015 had to do with actual footballs. Did New England Patriots quarterback Tom Brady orchestrate the deflation of footballs during the showdown with the Indianapolis Colts in the AFC Championship Game? Brady denied it, but the league handed him a four-game suspension, while the team was hit with a $1 million fine and the loss of a first-round draft pick. Of course, Brady and the NFL Players Association successfully appealed the NFL's decision, with U.S. District Judge Richard Berman nullifying the suspension. To the delight of Patriots fans and the dismay of many others, Brady was allowed to start Week 1.

The NFL is currently appealing the ruling. Since then, new rules and policies have been put in place to prevent madness like this from happening again. Whatever happens, we'll always have that hilarious courtroom sketch.

The most anticipated storyline of media day ahead of Super Bowl XLIX was this: What would the Seattle Seahawks' famously taciturn running back, Marshawn Lynch, say in his league-mandated appearance? His answer -- "I'm just here so I won't get fined" -- was delivered 29 times within the five minutes he was required to be there. We have to admire his consistency and determination to let his play do all the talking.

Unknown rookie New England cornerback Malcolm Butler introduced himself to the world on football's biggest stage with his fortuitous interception of Seattle Seahawks quarterback Russell Wilson in the closing seconds of Super Bowl XLIX. The interception saved the game for the Patriots, sending their fans into euphoria and Seattle's fans into questioning mode.

Butler's INT led many to passionately question Pete Carroll's decision to call for a pass on that final play. Many felt the situation -- second-and-goal from the one-yard line -- was best suited for Marshawn Lynch's power running game. Regardless of your rooting interest, Butler's play was a classic, ensuring another victory (and parade) for the Patriots.

March, for the NFL, is free agency season. Near the top of the list of free agents this year was Darrelle Revis and his island. Jets owner Woody Johnson wanted his former star cornerback to come back home, and Revis wanted a huge payday -- which he rightly deserved. Both Johnson and Revis got what they wanted. Other notable free agent signings included Ndamukong Suh, who landed with the Miami Dolphins for a record-setting (for a defensive player) $114 million, and running back DeMarco Murray, who went to the Philadelphia Eagles after rushing for 1,845 yards in Dallas.

San Francisco 49ers linebacker Chris Borland announced on ESPN's Outside The Lines in March that he was retiring from the NFL due to concerns about the long-term health effects of head trauma. The news was shocking because not many players have chosen to voluntarily walk away from millions of dollars in future earnings, even because of health concerns. Borland was not the only 49er to retire in the offseason, as linebacker Patrick Willis had called it quits a week earlier, and defensive tackle Justin Smith retired in May after a 14-year career.

Philadelphia Eagles head coach Chip Kelly brought in the former All-American quarterback, who had not played since an early 2013 preseason game for the New England Patriots, for a tryout. But Tebow Time ran out before the season's first official kickoff, as he was cut on the final day of the preseason.

Despite his failure to secure a final roster spot, fan support remained. His Eagles jersey (No. 11) was near the top 10 in sales from April to June. I can't decide if I should feel sorry for the folks who purchased this jersey or envy them for their potential collector's item.

The Tampa Buccaneers selected Florida State quarterback Jameis Winston No. 1 overall in the 2015 NFL Draft -- and the move paid off, with Winston throwing for 3,717 yards (fourth-most in by a rookie in NFL history) and 22 touchdowns against 13 picks through Week 16. Around the NFL writer Chris Wesseling called Winston "one of the best pure throwers to enter the league since Peyton Manning in 1998" whose "best selling point is assuming a leadership role as the youngest player" on the Bucs, transforming Tampa Bay "from a forgotten organization to one with an exciting future." Need I say more?

With the second pick, the Tennessee Titans picked Marcus Mariota out of Oregon. Both players look to be franchise caliber quarterbacks.

Pro Football Hall of Famer Frank Gifford passed away in August at the age of 84. Gifford played 12 seasons for the New York Giants, helping the team reach five NFL title games. Gifford's on-field performance earned him a place in Canton, but to many, he might be best known for his work in the broadcasters' booth calling NFL games. His transition from field to the booth helped pave the way for players looking for a second career. Gifford was loved by both the NFL fraternity and the entertainment community.

Redskins general manager Scot McCloughan announced the team would pick up Robert Griffin III's fifth-year option for 2016 at $16.1 million in April. Since then, he's attempted a total of 13 passes, all in the preseason. The 2012 Offensive Rookie of the Year has only suited up for one game in 2015 and never came close to seeing game action. Now we wait and see what the future holds for the quarterback.

The Dallas Cowboys' hopes of improving on a 12-4 2014 season were dashed when quarterback Tony Romo injured his collarbone in Week 2 against the Philadelphia Eagles. With their top signal caller on the shelf, the Cowboys lost their next seven games. Romo returned in late November, only to suffer a season-ending fractured clavicle in his second game back. Backups Brandon Weeden, Matt Cassel and Kellen Moore have combined to win only one of their 11 starts without Romo. Romo's injury clearly had an effect on the Cowboys' season.

On a chilly November evening, Packers great Brett Favre took in the roar of the Green Bay faithful.

Getting back to Lambeau was surely not easy for the gunslinger. The relationship between Favre and the team had been fractured by the handling of Favre's departure from Green Bay as a player following the 2007 season, leading to his eventual signing with the hated Minnesota Vikings.

Time and the most beloved Bart Starr helped heal the relationship. The return home for Favre was cherished by all in attendance, who cheered as the tarp fell to unveil the No. 4 on the Lambeau Field facade.

Green Bay is a better place when Favre has a spot there.

It took 60 minutes, a questionable facemask penalty and one untimed down for the Green Bay Packers to pull out a victory against the Detroit Lions in Week 13. Aaron Rodgers rolled left, then right, buying time for his receivers to get into the end zone. Given with the time and space, Rodgers launched the ball high into the indoor sky of Ford Field. Tight end Richard Rodgers found himself with a clear path to the football in front of the numerous Lions defenders, leaped up and snagged it for the winning touchdown, causing Packers players to storm the field in celebration.

Pieces of note: The 61-yard Hail Mary was the longest walk-off offensive touchdown in the NFL since 1983. Richard Rodgers' father, Richard Rodgers Sr., had a role for Cal in "The Play," throwing two of the five laterals that helped Cal beat Stanford in 1982 while the Stanford band was on the field. Strange how history can intertwine.

The Panthers won the NFC South in 2014 with a 7-8-1 record. In 2015, they chased NFL perfection until Week 16, when they finally lost to the Falcons. They've set a franchise record for wins in a season and became the first NFC team to start 14-0. They wrapped up the division in Week 13 and will have a first-round bye. And while the 1972 Dolphins can rest easy knowing they'll remain the only Super Bowl winning team to be undefeated, Carolina quarterback Cam Newton is solidly in the driver's seat for the MVP award.