Who’s on first, but, wait — what’s in the infield?

Mike Weaver was watching his son, Aiden, play with his fellow Libertyville Wildcats in the a Memorial Day tournament Saturday when out of the blue, with not a gust of wind in the air, a dust devil formed.

Weaver, 40, is a lieutenant for the Libertyville Fire Department in Libertyville, Ill., which is why he posted the video to the Libertyville Firefighters’ Twitter page. He says the firefighters try to post interesting things they spot happening in the community.

“We had a slight tornado delay,” Weaver wrote on Twitter. It wasn’t a tornado, but it was certainly a powerful dust devil.

It was a hot day with highs around 90 degrees, according to the National Weather Service. Dust devils are kind of notorious around baseball fields, perhaps because of how hot they get — especially when they’re surrounded by parking lots.

Dust devils form on very hot days when the air near the ground heats up rapidly — much faster than the air a dozen or so feet above the ground. The temperature difference makes the air unstable, because hot air rises and cooler air sinks. A dust devil is a tiny little low pressure system that forms because of the instability.

“The dust just started kicking up,” Weaver said. “[It] just kind of waited and then it formed that perfect tornado-looking shape.”

Weaver said everyone “just sort of watched it.”

Weaver has lived in Libertyville for about 10 years. He said other people at the park that day told him they have been coming to games there for their “whole life” and hadn’t ever seen anything like the dust devil.

Neither the uniformed 9-year-olds nor the spectators ever suspected they were in danger, and fortunately the dust devil didn’t cross over into the stands. They have been known to turn loose items such as lawn chairs and coolers into projectiles.

“Everyone’s like, ‘Oh that’s neat,’ ” Weaver said.

Weaver guessed that the dust devil lasted about two minutes, which is typical. They’re small in size and in duration.

And to all the weather folks out there criticizing Weaver for calling it a tornado when you hear him say “tornado timeout” in the video: He knew it wasn’t a tornado. He was just making a joke.

If it was a tornado, “we would’ve been running,” Weaver said.