Bubba Wallace's day unraveled in San Diego as he lost a wheel between Turns 9 and 10.
What happened?
The incident occurred late in the opening stage, bringing out a caution and ending one of the strongest runs of his season.
Radio transmissions captured the immediate frustration inside the No. 23 camp, with a crew member exclaiming, "There it went. You've got to be kidding me."
Why it matters for Bubba Wallace
The timing could not have been worse, as Wallace had looked comfortable throughout the weekend on NASCAR's new San Diego street circuit.
He consistently ran near the front and looked capable of contending for a top finish, making the setback particularly painful.
What comes next?
Under NASCAR's wheel-detachment policy, the No. 23 team was assessed a two-lap penalty, and two crew members will serve automatic two-race suspensions.
Instead of fighting for stage points and track position, Wallace found himself trying to recover from a significant deficit.
The setback was a major blow to Wallace's chances of building momentum in both the regular-season standings and the playoff picture.
On Sunday, Wallace had been one of the fastest cars on the track, spending much of Stage 1 racing inside the top five.
But the loose wheel changed everything, and Wallace's race became a fight to salvage as much as possible before the checkered flag falls.
Wallace's misfortune added another dramatic moment to NASCAR's first-ever Cup Series event at Naval Base Coronado.
The weekend had already delivered plenty of headlines, from Shane van Gisbergen's pole-winning performance to a fan being arrested after climbing fencing and entering a restricted area.
Now, one of Sunday's biggest stories belongs to Wallace, who will look to bounce back from the setback in his next race.