Football is finally back. No more training camps or preseason games. The real deal is upon us. The Chiefs open the season at home Sunday against the San Diego Chargers, and it is sure to be an emotional day for fans.

Not only is it the beginning of a highly anticipated season for the Chiefs, but it is the fifteenth anniversary of the terror attacks of Sept. 11, 2001. The Chiefs are planning to honor first responders and military members in the pregame ceremonies, that will also include a stealth flyover.

Kansas City enters 2016 with a few question marks lingering around, most notably the defense. Injuries to linebackers Justin Houston and Josh Mauga are key losses on the defensive side of the ball. Jamaal Charles' health figures to play a factor in Week 1, too.

Alex Smith and the rest of the offense are set to be the force of the team this season, at least initially. Smith had an impressive preseason, boasting a passer rating of 99.4 and completing 32 of 46 pass attempts.

Kickoff is slated for 12 p.m. CT and can be seen on CBS. Kevin Harlan and Rich Gannon will be on the call in the booth.

Here's three things to look out for in Sunday's game:

1. Linebacker and Secondary Play on Defense

It seems to be that the biggest concern from Chiefs players, coaches and fans is the defense. Specifically, the linebackers and secondary face the biggest doubts. At the linebacker position, veterans Derrick Johnson (left inside linebacker) and Tamba Hali (right outside linebacker) will be the anchor. However, both Johnson and Hali have been in the league for 12 and 11 years, respectively. Age, along with the wear and tear, will no doubt be a factor.

But the Chiefs have question marks surrounding the other two expected starting linebackers, Dee Ford and Justin March. March enters 2016 after spending the entire 2015 season on injured reserve. Ford started four games in 2015, and he has shown the ability to be a defensive force but has yet to excel to the next level.

Andy Reid has decided to go young at the cornerback position. Marcus Peters and Phillip Gaines have combined for just five years of NFL experience. Peters, who had eight interceptions in 2015, figures to be the stronger of the two.

Chargers quarterback Phillip Rivers will probably look to attack Gaines more than Peters. Gaines played in just three games in 2015, his second year in the league. He's yet to cause a turnover in his NFL career. Safety Eric Berry will play a significant role in how the Chargers attack the secondary, too.

2. Rookie Guard Parker Ehinger

The 6-6 lineman out of Cincinnati comes to the Chiefs as the 105th pick in the NFL draft. Parker Ehinger struggled at times in the preseason, most notably in the team's road loss at the Los Angeles Rams in Week 2.

In that particular game, Ehinger struggled against a dominate Rams defensive line. He struggled against both the run and the pass. A team's offense is so dependent on the offensive line, so it'll be key to watch how Ehinger responds Sunday in his first regular season game.

3. Running Back Position

It's possible (maybe even likely) that Jamaal Charles won't be ready in time to play Sunday afternoon. After suffering an ACL tear in 2015, Charles is still recovering. He has practiced, but Andy Reid is insistent on not putting Charles out on the field until he is 100 percent game-ready, which we probably won't find out until shortly before the game.

If Charles does indeed not play Sunday, Spencer Ware will likely get the call to start in the backfield. Ware is a reliable running back and could start on some teams around the league. In 19 carries against the Chargers defense, Ware averages 7.79 yards per carry.

And if Charles is ready to go by Sunday, expect Ware to still get a decent amount of carries. Here's the moral of the story: Charles probably isn't your most reliable choice for your Week 1 fantasy football lineup at running back.