Candlestick Park is 50% Giants fans today. There's never that many 49er fans at their away games.

You've likely got a lot of transplanted fans from New York in San Fran. That would be the only explanation unless 50% is an exaggeration. Usually the only teams that take over away stadiums are the Packers, Cowboys and Steelers. For obvious reasons, bandwagoners.

As time progresses the number of fans of Giants fans will further increase.