The center fielder for the El Paso Diablitos sandlot baseball team smacked a single and hustled to first in an April 2017 game in East Austin. That was when Texas Playboys first baseman and documentary filmmaker David Modigliani got his first up-close look at the lean and energetic man who had announced six weeks earlier that he was running to represent Texas in the United States Senate.

Beto O’Rourke had made good, solid contact in that early inning. But what he did during the seventh inning stretch really impressed Modigliani: The newly minted candidate hopped on a hay bale and gave an impromptu speech about the unique style of campaign he intended to utilize in his run against politics-as-usual.

Modigliani witnessed in that moment the charisma that would push O’Rourke's campaign into the national spotlight and earn him a place among the most popular Democratic Party politicians on the scene.

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The Barnstorming With Beto event that spring day offered an early look at a bootstrap campaign that would see the El Paso congressman visit all 254 Texas counties, speaking at first to groups of tens and later thousands. The grassroots campaign that pledged to take no money from political action committees or special interest groups and eschewed pollsters and consultants intrigued Austinite Modigliani, who made the 2008 documentary “Crawford” about George Bush’s effect on the small Texas town.

The graduate of the Michener Center for Writers at the University of Texas persuaded O’Rourke a couple of months after the baseball game to let him document the soon-to-be-famous campaign on film. The result is “Running With Beto,” a kinetic, intimate and moving documentary. The film makes its world premiere Saturday morning at the Paramount Theatre during South by Southwest and will air on HBO in late spring.

“I felt very early on, and a lot of people didn’t believe me at the time, that this is going to be an interesting story whether he wins or not,” Modigliani said. “From the outset, it seemed to most people, including me, that he was going to run an interesting campaign but that he was a total long shot and was unlikely to win. But it felt like he was going to approach it in such an interesting way that the national conversation was going to run through the middle of this race.”

Modigliani would prove to be prescient.

It might be hard to remember, but O’Rourke was a virtual unknown outside of his district when he started his U.S. Senate campaign. That was before he became an eccentric and accessible darling on social media and before video of his cogent and extemporaneous response to a question about National Football League players kneeling before the national anthem racked up tens of millions of views online.

Modigliani captures those early days, starting in the early fall of 2017, as the seemingly perpetually sweat-stained candidate faced tiny crowds armed with questions and offering only smatterings of applause.

The film follows O’Rourke into intimate settings, as he bounces from Sulphur Springs to Mineola to Waxahachie, and the loose verite style of shooting and framing, which matches O’Rourke’s exhaustive campaign style, puts viewers squarely in those often-tense rooms, where conversations are vulnerable and real.

Modigliani, a Massachusetts native, tackled his own preconceived notions of small-town life when he made “Crawford.” Informed by that experience, he knew that getting into these rooms with O’Rourke, who was often confronted with open pushback, could reveal to audiences the human side of politics. It was part of his pitch in landing the job several other filmmakers had attempted to procure before him.

“I told him that I found that connecting with those people as human beings first and talking politics second led to a really interesting dialogue and a really interesting tension within the film, and I would be excited to go with him to some of these really small towns to open up a dialogue,” Modigliani said.

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The documentary follows O’Rourke closely, viewing the candidate from backstage before major speeches and trapped in the car for long road trips between campaign stops. And while viewers may be familiar with some of those settings, they will likely be invited into an entirely new world when the film moves beyond the candidate’s point of view.

The word “with” is as important as “running” or “Beto” in the documentary’s title. Modigliani and his small team capture the hopes and frustrations of activists, organizers and supporters, weaving in their individual stories into the larger narrative of what really drives democracy. There’s the scene-stealing, straight-talking woman from Bulverde who admitted she had fallen asleep at the wheel and had been roused to re-engage and fight for veterans’ and women’s rights; a young student energized by his desire for stricter gun control; and a voter registration activist in the Rio Grande Valley who ran up against opposition within her own family. Each of their stories takes a personalized view of civic engagement, making personal the universal.

“Running With Beto” is as much their stories as it is O’Rourke’s.

“The film is about people responding to crisis in democracy and allowing themselves to be vulnerable and allowing themselves to participate in politics in a new way,” Modigliani said.

It is also a revealing portrait of the sacrifices made by campaign workers and O’Rourke’s own family, as their energies are tied to the ebbs and flows of a grueling campaign that demands much of all involved.

While the film elicits warmth with evocative and charming personal moments of O’Rourke reading “The Iliad” during his own journey or playing basketball with his children, it doesn’t feel canned or staged. “Running With Beto” never treads into hagiography, showing its candidate at once a doting but conflicted father and an open-minded yet sometimes frustrated boss to a Spartan staff largely composed of neophytes.

“I felt it was brave of him to give us the access that he did,” Modigliani said. “There is real conflict and tension, and there are moments, as you saw, where he doesn’t always come off as a prince. It just shows the realities of the stress on the campaign trail, the realities of stress and tension within the family. It has a realness that we were able to capture because of the access we were afforded. They were committed to running a no-BS campaign and we wanted to make a real no-BS film that captured that experience.”