With one regular-season game left to play and a 12-3 record heading into it, it's fair to say the Pittsburgh Steelers have had a good year.

They are AFC North champions, have a first-round bye headed into the postseason and still have a chance to take the conference's top seed in Week 17, which would give them home-field advantage throughout the playoffs.

So how did Pittsburgh get here? Here is the Steelers' year in review, highlighting the major moments in their impressive season.

Bell's Big Return

When Steelers running back Le'Veon Bell returned from his summertime-long contract holdout—finally signing his franchise tag to make him available to play in Week 1—he had missed all four of the team's preseason games and all of training camp.

The worry he would be rusty was real and seemed to be justified in Pittsburgh's season opener, when he earned only 32 yards on 10 carries and caught three passes for 15 yards.

Bell's slow start quickly evaporated, though, and the running back quickly regained his form as Pittsburgh's top rusher and a key receiver in the passing game.

Through 15 games, the Steelers have 409 team rushes for 1,543 yards and 10 scores; 321 of those carries, 1,291 of the yards and nine of the 10 touchdowns belong to Bell. The 25-year-old has also caught a career-high 106 passes, for 655 yards and two additional touchdowns.

Bell's number of carries is also a career high and something that should be monitored as the regular season gives way to the playoffs, especially given his backup, James Conner, is now on injured reserve with an MCL problem.

However, Bell's major contributions and ability to keep up an extremely high level of play while having so much asked of him was a hallmark of the Steelers' 2017 season.

Pass Rush Bounces Back

Though the Steelers' pass rush was not nonexistent in 2016. With the defense totaling 38 sacks, there was room for improvement.

This was achieved, in part, by the Steelers using their first-round draft pick on outside linebacker T.J. Watt, but it was enhanced by Vince Williams' promotion to starting inside linebacker and with it, an increased reliance on an interior pass rush.

The return of a healthy Cameron Heyward, who was limited to just seven games in 2016 with hamstring and pectoral injuries, also provided a major boost to Pittsburgh's ability to bring pressure this year.

Through 15 games, the Steelers defense has 50 sacks, the second-most in the league. They added seven in Week 16 alone. Heyward leads the team with 12, Williams has seven, while Watt and Bud Dupree have each added six. In 2016, their leader was James Harrison with five.

While Pittsburgh's pass rush isn't the only reason the defense ranks in the top five in both yards and points allowed—and is in the top 10 in every passing defense category—it's a big one.

Affecting quarterbacks before they can even get the football out of their hands means the play is a failure before it begins and pushes offenses backward and into and-long situations the Steelers can use to their advantage.

This key improvement has resulted in across-the-board improvements for Pittsburgh this season.

Ben Roethlisberger's Ups and Downs

Though the Steelers opened the first half of their season with a 6-2 record, not all was well on the offensive side of the ball.

Quarterback Ben Roethlisberger played erratically through their first eight games, struggling to score on the road and at home. He threw 10 touchdowns to nine interceptions in that span, including being picked off five times in a Week 5 loss to the Jacksonville Jaguars.

However, a switch flipped following the Steelers' Week 9 bye; since then, Roethlisberger has been one of the most effective quarterbacks in the league.

In September, he completed 62.73 percent of his passes, throwing five touchdowns to one interception. In October, he had a completion percentage of just 60, with five scores to eight interceptions thrown.

In November, though, his completion percentage rose to 67.77 percent, with 10 touchdowns thrown to three picks; in December, the 35-year-old has completed 66.67 percent of his passes, with eight touchdowns thrown to two interceptions.

The Steelers have thus lost only one of their last seven contests and Roethlisberger has thrown 18 touchdowns to five picks over that span.

Though the Steelers' season hinges on more than just the performance of one player, there is also no question that the quality of quarterback play is one of the greatest indicators of overall success in the NFL.

Where Roethlisberger was among those holding his team back earlier this year, he's now one of the reasons why they have secured a first-round bye and no lower than the No. 2 seed in the AFC.

Roethlisberger's 2017 campaign is a testament to a season being less about how it begins and more about how it finishes.

Antonio Brown's Injury

While both Bell and Roethlisberger have turned heads on offense this year, they were not alone. For the fifth year in a row, top Steelers wideout Antonio Brown has amassed over 1,000 receiving yards; it's also his fifth with over 100 catches in the regular season.

Pittsburgh's passing offense has been Brown-centric for much of the year. He has 101 catches for a league-leading 1,533 receiving yards and nine scores. He was also the league-leader in targets and receptions, until a lower leg injury suffered in Week 15 against the New England Patriots saw him leave the field in the second quarter.

He didn't play in the Week 16 win over the Houston Texans and isn't likely to suit up again until the Steelers take the field in the postseason, mercifully after a Round 1 bye.

There are silver linings to Brown's injury. One is that it is not season-ending, just serious enough to sideline him for the remainder of the regular season. The other is that the Steelers have myriad other talented players able to take up the slack.

From Bell's contributions as both a rusher and receiver to fellow wideouts Martavis Bryant and JuJu Smith-Schuster (who combined for nine catches for 145 yards and a score in Week 16) to tight ends Jesse James and Vance McDonald, Pittsburgh's passing game has stayed alive and healthy over the past two weeks.

However, there is no doubt Brown was a focal point of Pittsburgh's offense when he was healthy and his star is likely to dim somewhat even upon his return in the playoffs.

Brown won't be at full strength even if he feels good enough to suit up, and with some formidable potential opponents ahead, Pittsburgh's ability to mitigate this disadvantage may not go as well as it did against the four-win Texans.

The injury hasn't been a regular-season turning point for the Steelers, but it could be come January.

Ryan Shazier's Injury

While Williams, Watt, Heyward and even cornerback Mike Hilton have been the Steelers' major defensive players when it comes to the pass rush, no one has been more indispensable on that side of the ball in both coverage and run-stopping than Ryan Shazier.

The absence of the inside linebacker since suffering a scary spinal injury against the Cincinnati Bengals in Week 13, which has him currently unable to walk and using a wheelchair, has been notable on the field.

Shazier still has 89 total tackles, tied for the most on Pittsburgh's defense. His 11 passes defensed remain the team's second-highest tally, and he leads the defense in interceptions, with three.

Without him playing, though, the Steelers have had to scramble to find the right combination of players to take on his considerable role as the defensive leader. They brought back former Steelers linebacker Sean Spence and also moved outside linebacker Arthur Moats to the inside to help compensate, with the pair joining L.J. Fort and Tyler Matakevich as potential solutions to this significant problem.

The effects of losing Shazier are already evident. The Steelers have given up over 100 rushing yards in three of their last four games after only doing so twice between Weeks 1 and 12. They allowed 413 yards of offense to the Baltimore Ravens in Week 14, just the second time opposing offenses have surpassed the 400-yard mark against them this year.

While the Steelers can continue to lean on the other aspects of their defense that have worked well this season, particularly the pass rush, Shazier's importance as a player and a leader have only been further magnified by his absence.

It could prove troublesome for Pittsburgh once the postseason begins.

Martavis Bryant Drama

Martavis Bryant's standing on the depth chart took a hit during the 2017 offseason when Pittsburgh used a second-round draft pick on receiver JuJu Smith-Schuster.

Although it was Sammie Coates who was ultimately the biggest casualty of the signing—eventually traded to the Cleveland Browns—Bryant also saw his playing time take a hit, to the point where he was airing his grievances publicly.

For his efforts, Bryant was benched for one game, after repeatedly asking to be traded and declaring his unhappiness. And he wasn't entirely wrong to be upset.

Bryant, who caught 50 passes for 765 yards and six scores in 2015 before spending 2016 suspended for repeated violations of the NFL's substance abuse policy, was expected to be a major player in Pittsburgh's passing game as a game-changing deep threat.

For much of the year, though, his per-game catches could be counted on one hand. He has yet to post 100 yards in a game, and although he scored a touchdown in Week 2, he didn't find the end zone again until Week 12.

However, the injury suffered by Brown gave Bryant an opportunity to be a bigger part of Pittsburgh's offense, and he's done a respectable job of bouncing back. Though he's been outperformed by Smith-Schuster, who has 774 yards and six scores on 49 catches, he's not too far behind, with 44 receptions for 538 yards and three scores. 

Bryant has at least kept any dissatisfaction to himself as the season has progressed. What was once a major distraction for the Steelers has quieted considerably.

For a time, though, it seemed like winning games wasn't enough to keep Bryant happy and a one-man mutiny was underway. 

The Patriots Matchup

Though the Steelers had 13 games on the schedule leading up to their Week 15 meeting with the New England Patriots, there's no doubt that contest was the one most heavily circled in red.

The Steelers and Patriots have developed a rivalry thanks to both being among the AFC's top teams for over a decade, but New England has most frequently gotten the upper hand over its Pittsburgh counterparts, including twice in 2016.

While the Steelers did not have inside linebacker Shazier and lost receiver Brown in the second quarter, Pittsburgh still had numerous opportunities to defeat the Patriots in Week 15. But an inability to stop tight end Rob Gronkowski from marching down the field and a touchdown pass to tight end Jesse James—followed by a Ben Roethlisberger interception—sealed the Steelers' fate in a 27-24 loss. 

Since 2004, when Roethlisberger became the Steelers' starting quarterback, Pittsburgh and New England have met 12 times, including in the playoffs. Pittsburgh has won just three of those, most recently in 2011. That makes for five straight losses to the Patriots.

The two teams may meet again—perhaps in the AFC Championship, as they did a year ago. And while the loss didn't appreciably ruin the Steelers' postseason hopes nor their ability to clinch a first-round playoff bye, Week 15 could have been a chance for Pittsburgh to send a statement that they have failed to deliver for over half a decade.

The wait for the Steelers to get the better of the Patriots continues.

Releasing James Harrison

With the Steelers needing to make a roster move after right tackle Marcus Gilbert was reinstated from his four-game PED suspension, cutting someone was necessary. But it was the player the Steelers released that came as a major surprise: outside linebacker James Harrison, Pittsburgh's all-time sack leader.

It came as a shock only because of Harrison's legacy with the team, which began in 2002. Save spending 2013 with the Cincinnati Bengals, he had spent his whole career with the Steelers, and it seemed as though the 39-year-old would get to finish out the 2017 season wearing black and gold despite his limited usage this year.

Thanks in part to the Steelers drafting Watt in Round 1 this year and a shift toward putting their outside linebackers in coverage more often, Harrison was off the field more than he was on it.

He was active in just five games (partially owing to a back injury) and totaled just one sack and three tackles while taking part in a mere 4.36 percent of the Steelers' total defensive snaps. But it was long believed Harrison's pass-rushing prowess was being preserved for the postseason. If that's the case, he'll be doing so for a rival: the New England Patriots.

After visiting with the team on Tuesday, Harrison agreed to a one-year deal with New England, information initially broken by ESPN's Field Yates and others.

Now, it's possible Harrison will be staring down Roethlisberger rather than Tom Brady in the postseason. Will this be a mistake that dooms the Steelers in a month's time or merely a strategic play by the Patriots, a type of psychological warfare? 

No matter what comes of Harrison's stint with the Patriots, one thing is certain: his release was an unexpected one, regardless of his limited contributions this season. It was not how anyone envisioned his career in Pittsburgh coming to its presumptive end.