A slow-moving freight train stopped marathon runners in Lehigh Valley, Pa., on Sept. 11. (Lehigh Valley with Love)

To qualify for the Boston Marathon, one of six elite races known as the Major Marathons, runners need to prove their mettle. An average 26.2-mile run through the park will not do.

To enter your name into consideration for the 2017 Boston Marathon, you must first run a qualifying marathon at an impressive clip: A 35-year-old man would have to run each mile of his race in no more than 7 minutes 15 seconds — and this, depending on how fast other 35- to 39-year-old registrants are, does not guarantee he will be at the starting line in April. The last chance to run such a race is typically mid-September of the preceding year.

For runners looking to qualify late in the season, the Allentown, Pa., marathon offers an attractive option, as the course is largely flat; the marathon’s website boasts that it is a quicker race than many more popular Boston Marathon qualifying runs.

Sunday’s Lehigh Valley Health Network Via Marathon race course, as planned, crossed over a section of train tracks. The train, though, was not supposed be crossing the tracks at the same time as the runners.

But there it was.

About 8 a.m. Sept. 11, a “slow-moving” Norfolk Southern train cut through the marathon at the seven-mile mark, Sara Satullo at Lehigh Valley Live reported. Video of the incident shows dozens of racers milling about while the boxcars trundled by. For up to 10 minutes, runners watched as their chances of qualifying for Boston shrank. (There is some evidence that quick walking breaks may in fact be beneficial during a long run, but a 10-minute pause would be a problem for most competitive runners.)

A few marathoners reportedly jumped between the moving train near Allentown, Pa., but the rest were out of luck, and time.

“This is the tenth anniversary of this race, and all 10 races have crossed the Norfolk Southern rail tracks on Albert Street to enter Canal Park in Allentown,” Gerry Yasso, vice president of the nonprofit social services organization Via, said in a statement. “The incident is especially regrettable and was quite unexpected.”

The railroad knew about the race and agreed to halt any trains, coordinators for the marathon said. A representative for Norfolk Southern told Lehigh Valley Live it was “actively looking into who said what to whom.”

None of the nearly thousand race participants were injured by the train. But the Associated Press reports that runners like Charlie Young, 22, who were held up missed qualifying times.

Young was too slow by about 8 minutes. Marathoners took to running forums to voice their discontent, with one user writing, “It was a complete cluster as this mass of p—ed off people tried to get going again onto a trail the size of a sidewalk.”

In its statement, Via said that marathon times would be reevaluated “on a runner-by-runner basis.” It is unclear whether the Boston Marathon will accept the altered times.

Correction: A previous version of this post incorrectly stated the starting location of the marathon. It is Allentown, Pa.