“When I was growing up, I went to a Catholic school, and there wasn’t one Rangers fan in the entire school,” said Neil McGarvey, 43, who is involved in the operation of Kerrydale Street, a popular Celtic fan Web site. “It’s much more mixed now — my boy goes to a Catholic school, and there are maybe 5 percent Rangers fans now.”

Not surprisingly, emotions over the rivalry often boil over. Murders and countless assaults have been blamed on Old Firm tensions over the years, and the Scottish police have worked vigilantly in recent years after studies showed an increase in domestic violence on days when the teams played.

Businesses, too, are loath to favor one side. As has been the case for decades, the teams share a primary sponsor, the beer brewer Tennent’s. As many have noted, for a company to sponsor one team or the other would be fiscal suicide because half the consumers would probably boycott.

“It’s a rivalry that’s on so many levels,” Grant Russell, a reporter for Scottish Television, said in an interview. “It just all kind of comes together in this one game.”

“And now,” he added, “it seems it has gone away.”

Bocanegra said that Rangers players knew there had been questions about the club’s finances but had no idea of the situation’s gravity until they began reading about it earlier this year. The former owner, Craig Whyte, never spoke to the players until he went into the locker room one day in February, Bocanegra added, at which point Whyte announced that the team was going into administration — the British equivalent of bankruptcy — because of mounting debt and millions of pounds in unpaid taxes. Then, he left.

The players were shocked. Bocanegra is one of three Americans on the team, along with Maurice Edu and Alejandro Bedoya, and they have enjoyed being part of one of soccer’s greatest battles. When asked, Bocanegra often tells his American friends about what happened after one of his first Old Firm games, which Rangers won, 4-2.

After the match, Bocanegra and some friends went to a pub for dinner. Bocanegra thought he had slipped into the restaurant without being identified as a Rangers player, but when the waiter brought his meat pie to the table, Bocanegra looked down and laughed. The chef had carved into the top: “4-2 YES!”