PLANO, Texas—Just outside the town where Doc Holliday got in a major gunfight, Elijah Seybold and Nathan Waller stood back-to-back in silence.

A small crowd gathered nearby as an MC yelled, “One! Two! Three!…Pull!”

Then, Mr. Seybold and Mr. Waller pulled out copper-colored, electronic cigarettes, raised them to their lips, inhaled deeply and shot dense, white plumes of fog out of their mouths.

Two judges perched on stools nearby watched as the contestants’ foggy clouds traveled along a black measuring stick. As fans held their breath, Mr. Seybold’s cloud reached out all the way to 6 feet. Mr. Waller’s billowed out to about 5. As the judges pointed to Mr. Seybold, the crowd erupted in applause and cheers. “Sweet!” a spectator shouted. Mr. Seybold had won the first round in the Clouds for Heroes competition at the Metro Vapors vape shop.

Welcome to the newest entrant in the extreme sports category: “cloud chasing.” Competitors play it not with balls and bats, but with electronic cigarettes. They are called cloud chasers, and their devoted fans are cloud gazers.