Leave it to Dave McGillivray to do the unthinkable.

The longtime runner, race director and philanthropic-minded race participant first dreamed of competing at Fenway Park as a kid. But back then, he wanted to play second base for his beloved Boston Red Sox.

He first got the chance to run inside his favorite sports stadium in 1978 at the conclusion of his first transcontinental run across the United States—from Medford, Ore., to Medford, Mass.—to raise money for The Jimmy Fund and the Dana-Farber Cancer Institute. As part of the celebratory fanfare for his efforts, he ran two ceremonial laps inside Fenway Park before his Red Sox took the field to play a game.

The race director for the Boston Marathon for the past 30 years, McGillivray has organized more than 1,000 events over the past 35 years.

At 5 p.m. on Friday, Sept. 15, McGillivray will be one of 50 runners who will participate in the inaugural Fenway Park Marathon he is organizing. It’s the first marathon held entirely inside a Major League Baseball stadium, and it’s something McGillivray started dreaming about four decades ago and has been working on for six years.

“Just the thought of putting on an event inside Fenway entered my mind, and I thought, ‘Well, maybe I can sort of put on a 10K road race,’ ’’ McGillivray told Boston.com. “Then I thought, ‘Why a 10K? Why not do something more epic, like a marathon?’ ’’

Only 50 runners were accepted into the race, and each had to raise $5,000 for the Red Sox Foundation, the official team charity that focuses largely on youth programming and cancer research. In total, the runners raised more than $300,000 for the foundation.

The race will send runners on a 112-lap, USATF-certified course around Fenway’s dirt warning track. Each lap is 350 meters and will be recorded electronically. There is just one aid station that the runners will pass on every lap.

“I’m stoked to be running in this event,” says Hoka-sponsored athlete Michael Wardian, one of the fastest runners entered in the race. “It’s a totally unique event, which I love, and it raises money for a good cause. I love Boston and I love marathons and the chance to run a marathon at historic Fenway Park in front of the Green Monster was too amazing to pass up. The Boston Marathon is what got me into running and this race will be a celebration of that beginning.

The Red Sox are in first place in the American League East, but they aren’t playing in Boston this week. They’re on the road, playing at game at 7 p.m. Friday against the Tampa Bay Rays.

READ MORE: Boston.com