Negan's revenge tour swung by Alexandria on the midseason finale of The Walking Dead. And since Rick wasn't there to greet him, Carl stepped up to buy everyone some time to escape.
Carl seemed surprisingly confident while dealing with Negan in Rick's stead. In fact, Carl offered to die by Negan's hand if it meant no one else would get hurt.
While Negan spoke with Carl, the rest of the people in Alexandria were able to escape in trucks. And while the Saviors burned the town, Carl escaped into the sewers.
Later, Rick arrived in Alexandria just in time to duke it out with Negan in huge fist/bat fight. Apparently neither man knows how to swing bat wrapped in barbed wire. Despite several blows delivered on both men, they seemed only a little injured.
Rick escaped and rendezvoused with Michonne, who took him into the sewers to to meet with the group. While he was down there Carl revealed that he had a pretty bad walker bite on his ribs.
While the audience never saw the bite occur, it is theorized that is happened while Carl was fighting walkers with Siddiq in episode 6 from earlier this season.
The show runners have confirmed Carl's fate is sealed and that his bite will play out like previous bite victims.