PHILADELPHIA — Big Charlie’s Saloon in South Philadelphia seems like a perfect watering hole for watching the Super Bowl on Sunday. It is expected to be packed, but not with Eagles fans. It’s a Kansas City Chiefs bar in a passionate but parochial sports town that doesn’t exactly roll out the red carpet for fans of other N.F.L. teams.

“We’re in a pickle,” said Laura Sessa, the manager.

Ordinarily, it wouldn’t be an issue. There is no tense rivalry between the teams. Coaching and family ties bind them.

Andy Reid, the affable Kansas City coach, led the Eagles for 14 seasons and took Philadelphia to the Super Bowl. Travis Kelce, Kansas City’s gregarious tight end, is the brother of Eagles center Jason. Their mother, Donna, has been known to wear a customized jersey that mashes up colors representing both teams.

If an Eagles fan wanders into Big Charlie’s on any given Sunday, it’s no big deal. But the Super Bowl won’t be any given Sunday.

“It’s a little tricky now,” said Sessa, 54.

A bench is painted in Kansas City colors outside Big Charlie’s. A team flag flies on Sundays. Inside, the place is stuffed with helmets, mugs, autographed footballs, even an Emmy Award from a feature that N.F.L. Films did on the bar. There’s also a signed jersey from quarterback Patrick Mahomes and a replica of the Lombardi Trophy from the Super Bowl that ended the 2019 season.

For that Super Bowl, Big Charlie’s threw a block party complete with a disc jockey and fireworks as Kansas City defeated San Francisco, 31-20. This year, the watch party will be more subdued as a sign of municipal respect; it will be held entirely inside the bar — an island of red in a sea of green.

“I don’t want to instigate anything,” said Paul Staico, 57, the owner of Big Charlie’s. “This city is tough.”

So far, there has only been good-natured ribbing from Eagles fans.

“The mailman heckles us,” said John Alessi, 56, a Kansas City fan.

It has been suggested that wearing the jersey of an opposing team in Philadelphia is akin to putting a sign on your back that says, “Hit me.” In 1983, Eagles fans infamously plucked the feathers from the headdress of Washington’s unofficial mascot at the time, tore off his costume like drunken tailors, ditched his rubber spear and gave him a pugilistic send-off that required hospitalization.

But those were the loony days of long-gone Veterans Stadium. Sure, there is still the occasional and regrettable punching of a police horse (2018) and