The "Championship Belt" concept comes from boxing/wresting and is the idea that every season, the previous years champion (here the Super Bowl) starts with the belt, and each time they lose they pass the belt to the winning team who becomes the new sole owner.

The concept is explained here:

https://grantland.com/the-triangle/introducing-the-nba-regular-season-championship-belt/

So far this season, the Chiefs have lost this "belt" to the Lions in Week 1 (no, the preseason did not count), who then lost the "belt" to the Seahawks in Week 2. The Seahawks successfully defended their belt against the Panthers Week 3, and thus the Seahawks start this market "holding the belt" (but will pass it on after their first loss, if they lose).

The Pittsburgh Steelers currently hold the championship belt.

Week 0: Chiefs

Week 1: Lions beat Chiefs

Week 2: Seahawks beat Lions

Week 3: Seahawks beat Panthers

Week 4: Seahawks beat Giants

Week 5: Seahawks Bye

Week 6: Seahawks at Bengals

Week 7: Bengals Bye

Week 8: Bengals at 49ers
Week 9: Bills at Bengals

Week 10: Texans at Bengals

Week 11: Cardinals at Texans

Week 12: Jaguars at Texans

Week 13: Bengals at Jaguars

Week 14: Colts at Bengals

Week 15: Vikings at Bengals

Week 16: Bengals at Steelers

This market closes at the conclusion of the regular season, resolving simply with the team who holds the belt after Week 18. I'll update each week with the current owner of the belt. As a fun edge case, a tie would resolve in a division into two different belts (and could resolve for multiple teams).

Note that additional answers will not be added, so all teams not listed are contained in "Other".

Updated Market (that you can add answers to) is here: