Here's all you really need to know about the Giants-Athletics rivalry. When the two cross-bay teams met for real for the first time in the 1989 World Series, the hot souvenir was a baseball cap that was split down the middle -- half was an Oakland cap and the other half a San Francisco cap. That way fans could wear it and root for both teams, as if they were Hillary Clinton during an election year.

	Barry Bonds is by far the biggest attraction in the Giants-A's rivalry.

Fans may grow up in New York and Chicago rooting for two teams: their own and whoever is playing the crosstown rival. But it's different in the Bay Area, where most fans don't have such animosity between the two teams.

Which isn't to say there isn't a rivalry. After all, Oakland and San Francisco have been competing in baseball since the old Pacific Coast League, and that rivalry is still fresh in the minds of older fans. There is a rivalry that means a lot to local fans but it's just ... well, different. Like so many things are in the Bay Area.

"In some ways I think it's more of a Bay Area, Oakland/San Francisco thing than a team thing like the Mets and the Yankees,'' said Linda Vessa, a transplanted New Yorker who follows both teams religiously and regularly attends games in both stadiums. "There's just a natural animosity of lifestyle.

"San Francisco: a lot of white collars and white wine, the best address and the most difficult ticket in baseball. Oaktown: blue collar, beer, your city sold you out and put a football monstrosity in center field, and walk-up field level seats that are always available on game day -- even for playoff games.''

Although not for this weekend's series. During Thursday's game, Oakland announcers delivered a "ticket alert,'' informing fans that crowds of 45,000 to 47,000 are expected for this weekend's series. That's not surprising. For one thing, Giants fans see a game at the Coliseum as a chance to finally get a ticket to see their team play. And for another, East Bay fans tend to take the rivalry more seriously.

"Even though the A's have won four championships including one against the Giants, A's fans have a huge chip on their shoulder,'' Vessa said.

San Francisco fans, meanwhile, would probably dislike Oakland fans ... if they ever gave them any thought whatsoever. If the rivalry doesn't burn with hatred among the majority of fans, the players care even less. The area where the rivalry burns most intensely is in the front offices. The Giants staked out the Bay Area first and regarded the Athletics' move to Oakland suspiciously. For much of their history, the two teams have felt as if the Bay Area wasn't big enough for the two of them and both have threatened to move at one time or another.

	“	I root passionately for both teams because I'm a passionate fan. If I had to choose one team to root for, it would be, without hesitation, the Giants. Although it would hard to wish ill on the A's. ”
		— Linda Vessa, Bay Area baseball fan

More significantly, the Giants maintain they have territorial rights to the south Bay area, which is one location the Athletics have talked about moving if they could get a new stadium. That has created additional ill-will between the two front offices, an attitude best reflected in the Athletics' billboard of a couple years ago that had the slogan: "While they were building a ballpark, we were building a team."

You've got to love it when the marketing departments employ more trash talk than the players.

"As for me, I root passionately for both teams because I'm a passionate fan,'' Vessa said. "If I had to choose one team to root for, it would be, without hesitation, the Giants. Although it would hard to wish ill on the A's. So there you go again.

"I mean, I hate the Yankees and I more or less hate the Dodgers. Those are rivals.''

Jim Caple is a senior writer for ESPN.com.