We've heard a few times in the United Center, which has seen some championships in its day, "MVP and Coach" -- as in "Madame Vice President" and "Coach Tim Walz."

-ABC News' Rick Klein

Transportation Secretary Pete Buttigieg, who jokingly noted, "you might recognize me from Fox News," got cheers from the crowd when he criticized Sen. JD Vance.

Buttigieg, who like Vance is a veteran, particularly slammed the GOP vice presidential candidate over his previous comments that people who didn't have children weren't invested in the country's future.

"You know, senator, when I was deployed to Afghanistan, I didn’t have kids. Some of the men and women who went outside the wire with me did not have kids. But let me tell you, our commitment to the future of this country was pretty damn physical," he said.

Buttigieg has delivered this convention’s first extended takedown of Vance. That’s a bit surprising considering Vance is a pretty easy target for them: His average net favorability rating (favorable rating minus unfavorable rating) is -10 points, which makes him the least popular of the four people on the presidential tickets.

—538’s Nathaniel Rakich

"Here's a sentence I never thought I'd say, I'm Pete Buttigieg and you might recognize me from Fox News," he said as he introduced himself on stage.

Buttigieg frequently appears on the network to defend Biden-Harris policies.