Stuart football Coach Roy Ferri was in the checkout line at a Baileys Crossroads grocery store when he heard the cashier and the bagger openly debating which team would win the upcoming Stuart-Falls Church game that pitted their alma maters.

The schools’ “Bell Game” dates back five decades. Ferri did not disclose his affiliation for fear that the former Falls Church student running the register might jack up his bill.

“I was kind of curious to see if they [would] start throwing punches,” he joked.

Stuart-Falls Church, like so many Washington area high school football rivalries, still matters, whether the games are for provincial bragging rights (Madison vs. Oakton in Vienna), Catholic school domination in the District (Gonzaga vs. St. John’s, rivals that first met in 1889), poll-topping/recruit attracting (Good Counsel vs. DeMatha, teams that have finished atop The Post rankings seven times since 2000) or long-standing traditional tiffs (Episcopal-Woodberry Forest, since 1901) that transcend distance (87 miles separate the elite private schools).

In an era of colleges dumping conferences and longtime opponents for money-grab opportunities time zones away, and NFL players being discardable fantasy football pawns for many, high school rivalries are as passionate as ever because they usually include three of the basic indicators of meaningful relationships — similarity, proximity and familiarity.

In other words, local equals personal. If the Washington Redskins lose to the Dallas Cowboys, quarterback Robert Griffin III is unlikely to bump into Tony Romo at the gas station or the local gym. But it would not be out of the question for, say, Old Mill offensive lineman David Dunn to encounter Arundel wide receiver Tyler Young at a restaurant somewhere along the seven miles that separate their campuses in Anne Arundel County.

“My assistant coaches drive by the other Arlington County schools and see [the teams practicing],” Yorktown Coach Bruce Hanson said. “You’re not spying on them, you’re just driving.”

Local rivalries are about where you go to school. Or where your parents went to school. Or both. Children usually know what high school they will attend, so that emotional affiliation becomes ingrained early, sometimes through older siblings.

Players can grow up competing against the same peers in youth leagues and middle school before meeting on the grand stage on Friday nights or Saturday afternoons in high school. Middle school classmates can feed into rival high schools, heightening the “familiarity” part of the equation.

With rivalries, it’s all about inter-group comparison, said Christian End, a psychology professor at Xavier University in Cincinnati who researches fandom. And when it comes to high school sports, the personal stake often transcends my-team-beat-your-team joy and disappointment. It runs deeper because it’s more difficult to distance yourself from a loss based on the proximity of the opposing group.

It’s not only a team you’re pulling for, it’s your school or child or brother or some other first-hand bond, so more of you is wrapped up in the outcome. That’s unlikely to be the case at higher levels of football, where that personal connection is largely absent and team members hail from all over the country, not one town or neighborhood.

“Those dual identities can increase the intensity,” End said. Unlike pro and college teams, “this is no random group of strangers I have no affiliation with other than I choose to root for them. You may actually be a member of the organization compared to one that’s just supporting them financially and with crowd noise.”

The makeup of those crowds is another aspect of high school football that makes rivalries feel more immediate. At a professional or college football game, where one team is often traveling a great distance to play, the spectators are predominately rooting for the home team.

A high school game’s attendance is going to be closer to a 50-50 split, which means that supporters of each team are more likely to encounter each other during their everyday lives, a dynamic that increases the scope of their interest in the outcome.

In a sense, each of the opponents in a high school rivalry is the home team. Gaithersburg Coach Kreg Kephart, a 1973 graduate of that school, knows all about that from his days of playing Rockville school Richard Montgomery.

“Whoever won that got to go to the Hot Shoppes at Congressional Plaza and talk trash for a year,” Kephart said. “If you were in a barbershop in Rockville and Gaithersburg lost that year, you were going to hear about it. It’s community rivalries as much as [football rivalries]. It gives the fans something to care about that they don’t necessarily have those other nine games of the year.”

West Potomac and Mount Vernon are taking that community involvement one step further this season for Thursday’s “Battle for the Highway.” The schools, about four miles apart and with blurry enrollment boundaries along Richmond Highway (Route 1) in the Alexandria section of Fairfax County, scheduled a joint pep rally for Wednesday night.

They are partners in other ways, too. A community group is working to have turf fields installed at both schools.

“There are so many kids that have cousins and family that go to Mount Vernon,” said former West Potomac Coach Eric Henderson, who attended Fort Hunt High, which later folded into West Potomac. “It’s one of those deals where for 364 days you hang out and live with Mount Vernon kids, and then that one day of the year it turns into that backyard war.”

Matthew Paul, a senior quarterback-linebacker at Douglass, has grown up with an aversion to rival Gwynn Park, the Eagles’ annual opponent in the “Battle of Route 301” in Prince George’s County. Paul said he has seen Gwynn Park players while shopping at Target, but that they just give each other a look of respectful acknowledgment without any chitchat. There’s no need for it.

“Around the first week of school, everybody always asks, ‘When you all play Gwynn Park? When you all play Gwynn Park?’ ” Paul said. “Any time it’s a Douglass and Gwynn Park game, they stop what they’re doing no matter where it’s at, how much it costs.”

He’s not kidding about the ticket price. Douglass Coach J.C. Pinkney was at a Calvert Hall-Friendly game in late October 2005, chatting with Gwynn Park Coach Danny Hayes. Both men were wearing gear from their respective schools. Because Douglass had been bumped up a classification, that season was the only one in recent memory that the teams were not scheduled to play each other.

A man, spotting the school names or logos on their clothes, approached.

“This is the game I want to see!” he said. “I would pay $20 to see those teams play!”

Others probably felt likewise. At the time, both teams were unbeaten; Gwynn Park was amid a 14-0 season and Douglass would finish 12-1. Both teams outscored the opposition by more than 350 points that season.

“Danny and I just started laughing,” Pinkney said. “We wanted to play each other that year, too. Because it’s always fun. The one year I felt like it probably would have been the biggest game in maybe the history of our rivalry was the year we didn’t play.”