Nathan Patterson went to a Colorado Rockies game on July 15 and tossed a few four-seamers at the Coors Field radar booth. Now he’s a prospect in the Oakland Athletics’ farm system.

Patterson, 23, hit 96 miles per hour multiple times on the radar gun that afternoon in Colorado while watching the Rockies get walloped by San Francisco.

“A few days later the A’s gave me a call,” he told MLB.com. And this week, he signed with the MLB franchise.

His pro baseball journey is almost a year in the making. Attending a minor league game in Nashville last August, he hit 96 mph on the gun, too. It surprised him, he told MLB.com, because though Patterson pitched in high school, he didn’t pursue the game in college. It had been years since he pitched seriously.

Inspired by the newfound velocity and rested arm, he started training, joined a men’s recreational league to stay sharp, then heard from the A’s in February.

As he continued to train, he posted his pitching videos on social media, tagging MLB pitching evaluator Rob Friedman and his online prospect showcase “Flatground” to show off his progress. He developed a slider in the 80-mph range. His fastball consistently hovered in the low 90s.

Friedman, known as the “Pitching Ninja,” who between his three baseball-related Twitter accounts has roughly 192,000 followers and whose thoughts appear regularly on ESPN national baseball broadcasts, likens Patterson to Oakland all-star closer Blake Treinen. He told The Post that he sees similarities in the two pitchers’ smooth arm action and easy velocity.

Patterson could be a valuable prospect for the A’s because his arm is so fresh, Friedman added. He didn’t log three or four years of college baseball to potentially sap the life out of his pitches.

Oakland has yet to assign Patterson to a minor league team. He tweeted Friday that his new goal is to develop and make the big league roster.

“The stories have been incredible and I hope to inspire others,” he wrote. “I have been given an incredible opportunity.”