During the past two years the San Francisco 49ers and the Seattle Seahawks have formed the NFC's best rivalry.

And, as with any good rivalry, the intensity has spilled over from the gridiron into the stands. While we'll see stories about other opposing fan bases every now and then, Seattle and San Francisco supporters have been engaged in a constant back and forth this year unlike anything we've seen in recent years.

The needling started before the season, with reports that Seattle fans were looking to buy a brick outside the new 49ers football stadium and write a pro-Seattle message on it. According to a Nov. 18 story on SeattlePI.com, those fans have successfully purchased the brick.

The threat of violence in the stands was so serious ahead of the teams' first matchup on Sept. 15 that Seattle police dressed up as San Francisco fans in order to prevent any outbursts.

Then, for the teams' second matchup Sunday, a group of 100 Seahawks fans pooled their money and purchased a "Go Hawks" banner to fly around Candlestick Park before the game.

Not to be outdone, 300 49ers have combined to pledge nearly $8,000 to erect a provocative billboard near CenturyLink Field. The banner shows Dwight Clark's famous 1982 catch in the background and five Super Bowl trophies in the foreground. The text reads, "How many do you have?"

The group is hoping to have the billboard up at some point in the next few weeks.

A new commercial for "Beats by Dre" depicting San Francisco quarterback Colin Kaepernick wading his way through a swarm of vicious Seahawks fans has only served to make things worse between the fan bases.

If this is what the hype is like during the regular season, we can't even imagine what would happen should these squads square off in the playoffs.

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