What happened: Four weeks into the NFL season, only three teams maintain perfect records. The Kansas City Chiefs, Minnesota Vikings, and San Francisco 49ers are the league's remaining undefeated teams.

Why it matters: The separation establishes the front-runners across both conferences. The Chiefs maintain their momentum in the AFC, while the Vikings and 49ers remain unbeaten in the NFC.

What to watch: All three teams will attempt to protect their perfect records heading into Week 5.