Cram a football stadium with tens of thousands of fans of all ages, medical conditions and levels of rowdiness, and almost anything can happen.
And it does. Fans come down with heat exhaustion and strokes. They trip and break bones, and they sometimes have heart attacks.
Game day can get even more exciting when Mother Nature steps in. In 2001, lightning briefly emptied the stadium when a storm hit Norman during the fourth quarter of the game against North Carolina. Oklahoma State University has had similar almost-predictable brushes with bad weather. But when Mother Nature sent an unexpected plague of crickets to Stillwater more than a decade ago, fans scurried as the bugs rained down during a game.
The health and safety of 145,000 people - 85,000 at the University of Oklahoma and 60,000 at OSU - rest in the hands of paramedics, nurses, doctors, police, bomb-sniffing dogs, weather watchers and other emergency workers.
"Anytime you have 85,000 people at one location, you have the potential to have more than one need occur at the same time," said Kenneth Mossman, OU athletic department spokesman.
Just as the football players strategize, condition and plan in the months and weeks before the opener, the universities prepare well ahead for those emergencies.
Teams trained to attend to medical emergencies and equipped with a first- aid kit and automatic defibrillators are interspersed throughout the OSU stands, said Floyd Cobb, OSU fire marshal and assistant director of environmental health and safety.
Four nurses' aid stations are posted in the stadium. The staff typically includes a registered nurse hired from the local medical center, an administrative person, and someone trained to administer cardiopulmonary resuscitation and first aid.
When bad weather and football games collide, finessing massive crowds can become even more difficult.
"One of the biggest challenges we face is what do we do if a tornado is coming?" Cobb said.
Similar to OU, OSU has a weather specialist in the command post to watch the weather satellite system. University representatives use the stadium public address system or digital printout screens to announce approaching bad weather.
The closer the bad weather gets, the more urgent the message that fans should leave and find shelter. At some point, emergency workers have to make plans to get fans under the limited space in the west end zone, Cobb said.
"That's going to be a challenge to get that many people under shelter," he said.
Mossman said there's quite a bit of room under OU's stadium that is fairly well protected by concrete, but there is no real safe room.
He said the fire department parks its vehicles under the stadium but moves them on game days.
Besides space, time is another limiting factor in trying to keep fans safe. Cobb said it takes about 15 minutes to empty the OSU stands.
Weather risk management firm WeatherData sets a 20- to 30-minute benchmark for stadium evacuation, a range that Mossman called feasible for the OU crowds. The university had to evacuate the stadium a couple of times in recent years because of lightning, Mossman said.
"Lightning is probably our greatest enemy this time of year," Mossman said.
Lightning, tornadoes and floods have all bypassed stadiums but hit campuses, where crowds are gathered in a relatively compact space.
A twister touched down in 2005 just three miles west of the Iowa State University stadium just before the team played the University of Colorado. In 2001, two women were killed when a tornado raked across the University of Maryland campus. Floodwaters in 1998 damaged part of Colorado State University.
Now, OU, OSU, Iowa State and the University of Maryland have all joined the National Weather Service's StormReady designation, a national storm communication and coordination system that includes 75 areas in Oklahoma. Cobb and Mossman said keeping the huge crowds safe is a challenge, but the universities are ready for any emergency that might pop up with today's season openers.
The heat in the stadiums won't match the heat on the fields today, but Cobb and Mossman said fans need to watch out. They said the stadiums have cool zones with electric fans, but heat stress still is usually the biggest challenge in the stands during the season opener.
Fans should be aware of the weather conditions and prepare with lots of nonalcoholic liquids before and during the game, wear cool clothing when it's hot and extra clothes when it's cold, Cobb said.
"Just be mindful of the weather," Cobb said.
"I take my job seriously," he said. "I just want to make sure everyone has an enjoyable experience and that they're safe."