Kyle Larson chose the Indy 500. But rain, penalty spoil attempts at historic day.

INDIANAPOLIS — Kyle Larson rolled his Arrow McLaren Chevy to a stop on pit road, climbed out of the driver's seat, pulled off his helmet and let his disappointment show.

NASCAR's Cup series leader is the latest driver to attempt "the Double," racing the Indianapolis 500 and the Coca-Cola 600 on the same day. In this moment between races, doing so was still his intention, despite the fact the 600 was already underway.

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But as he shook his head before Tony Kanaan put an arm around him, what became clear was the day wouldn't quite be the storybook version he'd been building up in his mind.

"I'm proud to finish, but I'm pretty upset at myself," Larson told NBC after the race. "If I could have executed a better race, you never know what could have happened."

Larson finished 18th in Sunday's 108th running of the Indy 500 after a speed violation on a pit stop on Lap 134 took him out of contention.

“I smoked a left run or something heading into the green flag stop and killed our opportunity," Larson told NBC.

The day was already maligned as he waited out a four-hour rain delay and decided to prioritize the 500 over the NASCAR race where his attempt at a second Cup title in four seasons was on the line. The forecast of the recent days delivered with buckets of rain starting just before the race was supposed to start, and it became clear Larson would not come close to matching Tony Stewart's 1,100 total miles driven between the two races.

It's a situation he called a "worst-case scenario" before the race, but he chose in that moment to prioritize the 500, the bucket-list event he'd never tried before.

The green flag finally came down at 4:45 p.m., or just 75 minutes before the 600 was set to begin. Larson started in the fifth spot and gradually built up momentum, reaching as high as a fifth-place spot a quarter into the race.

But he was flagged for the pit road speeding violation, and it became clear by then neither of his dreams were coming true. He wasn't going to race the 1,100 miles of the endurance challenge and he wasn't going to top Stewart, Robbie Gordon or Kurt Busch, who hold the best 500 finishes while attempting "the Double," as each finished in sixth place.

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Larson was technically in the lead with a handful of laps remaining, but he was due to make a final pit stop. That dropped him to 18th place, where he finished 11 seconds behind the champion, Josef Newgarden, who won for the second year in a row.

Larson's attempt to do all of this, and to wait out a massive rain delay despite the risk to his NASCAR playoff standing, made an impression on some of his fellow drivers.

"I think it speaks volumes for the Indy 500 that he stayed," Newgarden said. "I think it shows the significance of this event.”

Said Pato O'Ward, Larson's McLaren teammate who finished second to Newgarden, "I think it'd be fantastic to have him back."

Larson is the ultimate competitor, the type of racer who will spend an off day during preparation for these two races at a dirt track at the Kokomo Speedway to compete in sprint car racing. He was determined to check this race, in this car, off the list, and he did that.

Soon, the focus will be doing it the way he wanted to.

"I would definitely love to be back next year," Larson said.

And then NASCAR's No. 1 driver turned back toward the track, dipped into the back seat of a black SUV to catch a plane to his second race of the day.

Contact Nate Atkins at natkins@indystar.com. Follow him on Twitter @NateAtkins_.

This article originally appeared on Indianapolis Star: Rain, penalty spoil Kyle Larson's attempts at historic Indy 500 day