The 2016 Denver Broncos season ended in disappointment, as the defending Super Bowl champions failed to even reach the NFL postseason.

We knew that it wouldn’t be easy, as the Broncos roster suffered a number of offseason losses. Starting quarterback Peyton Manning retired, and teams from around the league poached the Broncos free agents, in an attempt to capture some Super Bowl magic.

Yet the Denver defense remained largely intact, and Bronco fans were hopeful that this team could overcome the infamous Super Bowl hangover that has been plaguing NFL teams for decades.

After a getting off to a 4-0 start, Denver would lose seven of their final 12 games, and stumble to the finish with a 9-7 record. As we look back at the roller coaster season, we can find a number of key instances that played a huge role in the Broncos coming up short in the end.

Here are five key moments that caused the 2016 Denver Broncos season to go off track:

1. August 15, 2016: Defensive lineman Vance Walker is lost for the season with a knee injury

When Malik Jackson departed for Jacksonville in free agency, the Broncos were looking for someone to take on a bigger role on the defensive line. Eight-year veteran Vance Walker was tabbed to be the guy. Walker had been named a starter after putting together a solid 2015 season. He had logged 33 tackles with two sacks, and would be looking for more with the additional playing time. But in a nine-on-seven training camp drill Walker went down with a torn ACL, and was placed on injured reserve. The Broncos defense was still solid, but the depth on the defensive line had been compromised, and the team would eventually feel his loss.

2. October 9, 2016: The Broncos suffer their first loss, and following the game, head coach Gary Kubiak is hospitalized with a ‘complex migraine’

Denver had started off the season with four straight wins, but in Week 5, the Atlanta Falcons’ high-powered offense came to town to test the Denver defense. Falcons quarterback Matt Ryan managed 267 yards passing, and the Broncos lost for the first time 23-16.

But it was what happened after the game that may have changed the trajectory of the season.

For the second time in three years, head coach Gary Kubiak suffered a health scare, and was taken to a local hospital where he was diagnosed with a complex migraine. Kubiak would sit out the Week 6 loss to the San Diego Chargers, and would retire following the season to focus on his health.

3. October 24, 2016: The Broncos beat the Houston Texans, but lose running back C.J. Anderson for the year

After back-to-back losses, the Broncos would face the Houston Texans in Week 7, and a familiar face. After spurning the Broncos for more money in Houston, Brock Osweiler returned to Denver. The former Broncos backup quarterback was given a very unfriendly welcome, much to the glee of Denver fans. Osweiler was just 22/41 for 131 yards, and the Broncos won easily 27-9. But running back C.J. Anderson was lost for the season with a knee injury, and the Broncos struggling running game actually got worse. With Anderson out, it became more apparent that the offensive linemen signed in free agency were not working. Bronco quarterbacks were sacked 40 times in 2016, and the Broncos running game would finish the season ranked 27th in yards per game.

4. November 6, 2016: The Oakland Raiders run roughshod through the Orange Crush

It was the matchup that everyone had been waiting for. The 6-2 Broncos would square off against the 6-2 Raiders for the inside track in winning the AFC West. The Raiders would win the game 30-20, but the final score didn’t show how humbling of a loss that this would be for the Denver defense. Oakland rushed the ball for 218 yards, and controlled the ball for over 41 minutes. The season still had a long way to go, but it was apparent that this Broncos defense wasn’t quite as good as it had been, and the rest of the AFC had caught up.

5. November 27, 2016: The Broncos surrender an eight-point lead, and lose to the Chiefs in overtime

While the Broncos would still be in the hunt for a playoff spot until Christmas night, this was the game that sunk the season. The Chiefs and Broncos were tied at 7-3, and this game would prove to be vital to the push for the playoffs.

After trailing the Chiefs for the first half of the game, the Broncos scored three second half touchdowns to take a 24-16 lead with three minutes to play. The Chiefs offense had struggled all night, and the Denver defense could finish them off now.

Then Alex Smith drove the Chiefs 75 yards, and converted the two-point conversion, to take the game into overtime.

Following an exchange of field goals, the Broncos faced a 4th and 10 at the Kansas City 44-yard line, with just over a minute to play. Head coach Gary Kubiak opted to try a 62-yard field goal, instead of settling for a tie. The Brandon McManus kick would fall short, and the Chiefs would drive for the winning field goal.

The Broncos would continue to fight for a playoff spot until Week 16, but it would be on this night that the season was lost.