The 49ers and Seahawks has always been one of the most intense rivalries. It hasn't been a very long rivalry like the Cowboys v Eagles, and the Bears v Packers, but nonetheless it has probably been one of the most intense rivalry over the last decade
The coaches back in the day
This rivalry was ignited in the early part of decade. The 49ers had hired Jim Harbaugh, and the Seahawks had hired Pete Carroll. Those 2 coaches, had already had a rivalry prior to joining the NFL because they were rivals in College Football when Jim harbaugh was the Stanford Coach, and Carroll the coach of USC.
The 2 teams were on the come-up. The 49ers were already a SB contender, and the Seahawks were not very far behind at all. The 49ers and seahawks during the Harbaugh era, were always fighting close games, and the fans absolutely despised each other. During the 12-13 season the 49ers came of a NFC championship loss, and ended up in the Super Bowl that year, meanwhile the Seahawks drafted future Hall of Famers, Russell Wilson, and Bobby Wagner, and good pass rusher, Bruce Irvin in that draft class. Seattle was on the come-up, and were already giving the 49ers problems.
In the 13-14 season, it came to a head. The 49ers and the Seahawks were the best teams in the NFC undoubtedly, and were both the hottest teams in the league coming into the playoffs. The Seahawks with a record of 13-3 were the 1 seed, and got a bye, and the 49ers, came in as a Wild Card. As fate would have it, the 49ers cleaned through the playoffs, and the seahawks won their first matchup and they ended up in the NFC championship game against each other.
This game had everything, Questionable calls, Incredible Defense, and devastating injuries. The game ended with one of the greatest plays of all time, with “ The Tip” by Richard Sherman, sealing and clinching the win for the Seahawks, and that season ended with them winning the Super Bowl.
Back from the dead
The 49ers started to break up, and started to struggle, but the fan intensity remained. For almost 5 years the 49ers were not good at all, and suddenly in the 19-20 season, the 49ers jumped out of the blue, and went from the 2nd pick to the Super Bowl. The 49ers x Seahawks rivalry came right back. The fan intensity was back, and both games they played were nail biters which both ended in the last 10 seconds of the game. In Week 17, the season finale, the last game of the decade, the game to decide who won the division, and a game that would have MASSIVE ramifications on the playoff seeding, ended with one of the most incredible stops of the decade to win the game.
Now that both teams are good, and are both Super Bowl contenders, the rivalry is back, and bigger then ever. Hopefully it's here to stay.