Never mind that King had been instructed by her college coach before the race to "take the high road."
"That's what I told her," Ray Looze, who coaches King now at Indiana University, said late Monday night. "'Don't say anything. Don't get involved. Let's let our actions speak louder than our words.' But they're adults, and they have opinions."
King appeared to have made a conscious decision to turn her race against Efimova into a personal crusade. It may have started accidentally - when King's finger-wagging gesture at Efimova during Sunday night's semifinals was caught on camera, ensuring that King would be asked about it afterward - but at each opportunity, when given the chance to back off, King instead doubled down.
"You've been caught for drug cheating," King told NBC on the pool deck Sunday night, when asked about Efimova. "I'm not a fan."
Monday night, King didn't back down: "I stand by what I said. I said what everyone else was thinking."
King's fiery, vocal stand against Efimova surprised Chapman not in the slightest, and neither did the head-to-head victory that followed - when a loss would have been devastating, given the emotional stakes.
"We all said, 'Oh, if she doesn't win, this is going to be bad,' " Chapman said. "But I don't think losing ever crossed her mind. After it was over, her mom said, 'Did you think that goofy little girl was someday going to be a gold medalist?' Well, she did - Lilly did."
When King left the pool deck after her victory and entered the U.S. team area near the warm-up pool, she was greeted by Katie Ledecky, a two-time Olympic gold medalist, who grabbed King and screamed, "You beat her! You beat her!"
"I think that's the moment," Chapman said, "when it really sank in for Lilly that she'd done something big."
Where does this Midwestern teenager - a rookie Olympian and first-time participant at a senior-level international meet - come off anointing herself the sheriff of the doping police? It surely all stems from King's intense competitiveness, which everyone who knows her recognizes and which King herself readily acknowledges
"People probably think I'm serving it up a little bit, but that's just how I am," King said Sunday. "That's just my personality."
Now, she swims (against Efimova again) in the 200 breast Wednesday, with the final Thursday, refusing to quiet down even if many in the international media have questioned her sportsmanship.
"I'm not this sweet little girl," she said. "If I need to stir it up to put a little fire under my butt, then that's what I'm going to do."
But it has taken years, and an implausible journey in a sport where talent is almost always spotted early, for King to get to this point. She was not always seen as an elite swimmer. She didn't reach a state-level meet until age 12, or a junior nationals meet until 14. At one point, King was not only a Sea Creatures swimmer - but its self-appointed mascot as well. She would slide into the homemade green spandex costume, with its fins and mask, and walk around making people smile.
"She and her mom made this Sea Creatures costume, and she'd come to the little kids' [practice] session and dance for the kids," Chapman said. "And nobody told her to do that."
As a swimmer, she was a small fish in a very small pond - a far cry from the age-group phenoms whose rises to international fame everyone can spot from years away. At Lloyd Pool in Evansville, six high schools shared the facilities, which meant King's school, Reitz High School, was typically given just four lanes for its 35 swimmers to share.
"You do the math. It's not a lot of room to swim," King said at the U.S. Olympic trials in June. "I was just not training with a lot of people that were at my level and that could even train with me."
To make up for the lack of training, King would show up in the early mornings, when the pool was reserved for an adult masters team, and swim alongside the middle-aged plodders and wannabes. The extra training seemed to work, and by her early teen years, she began rising through the ranks of Indiana's best swimmers.
"At the first meet where she was seeded first, she was nervous. I'd never seen her like that," Chapman recalled. "But she raced and she won, and I went over to her and I said, 'Lilly, I'm real proud of you. You had adversity and you fought through it and won.' And she gave me the dumbest look and said, 'I wasn't going to lose.' "
Eventually, King became good enough to attract the attention of Looze at IU, where she entered as a freshman in 2015 and almost immediately began showing remarkable improvement.
"I hadn't even really done breaststroke training at all, and I hadn't even done races when I got to college - so just adding, literally, everything I possibly could on this year was a huge help," she said. "I finally had people to train with and race at practice and. So, I'm doing . . . almost double [the training load] I was doing before I got to college."
By this June, it was no longer considered an upset when King, ranked first in the U.S. by more than a second, won the 100 breast at trials to qualify for her first Olympic Games. By the end of the meet, she had added a second victory in the 200 breast. Some six weeks later, the world got to see the Lilly King that King's family and her coach know.
"When she kind of got on the world stage, everybody always talked to us about how polished she seemed," Chapman said. "And we were just thinking, 'Someday the real Lilly's going to come out - that girl who says what she means and doesn't care what anybody else thinks.' "
