Roger Dixon, president of the Metropolitan Entertainment and Convention Authority, said security personnel have made it a priority this year to keep fans from disrupting games at TD Ameritrade Park.
"While we understand this may be viewed as just having fun, we want guests to understand that it is a safety and security issue and fans on the field cannot be tolerated," Dixon said.
The CWS begins Friday and runs through June 25 or 26.
Officials for decades have winced at beach balls floating out of the stands onto the field. But they want to nip what has been an increasing number of fan-on-the-field incidents in recent years.
The breaking point came last year when several young fans hopped the 8-foot outfield fence in the seventh inning of Game 1 of the finals. According to media reports, six people were ticketed, including a 17-year-old girl who patted the backsides of two players while grounds crew members and security personnel chased her.
Omaha city prosecutor David Smalheiser said trespassers face up to six months in jail and a $500 fine.
New signs warning fans to stay off the field have been placed around the ballpark.
Dixon said it was discovered after the fact that plans for last year's CWS finals incident had spread on Twitter.
"I just think they're kids who get hopped up," Dixon said. "They're out here tweeting back and forth, talking about it, egging each other on. So we will start watching that now and when we see something like that building up, you'll probably see a bigger presence of security out there."
NCAA vice president of championships and alliances Dennis Poppe said fans who try to draw attention to themselves by running onto the field are spoiling what is a once-in-a-lifetime experience for many players. Poppe said he hopes the warnings dissuade potential pranksters.
"Frankly, you can't stop idiots," he said, "but you can do everything you can to make sure there isn't an interruption to the games."