No. 3: Fred Dean
To this day, the fact that the Chargers traded this guy away hurts. It created a snowball effect that led to several players ending up in San Francisco. As mentioned before, Gary Johnson went to the Niners as did Louie Kelcher and Billy Shields, all great players.
That all started with Dean, who demanded to be traded by the Chargers in 1981. As the story goes, Dean claimed that his brother-in-law, who was working as a truck driver, made more money than he did in San Diego.
Chargers ownership, against its best judgment again, sent Dean to the 49ers. He would become an instant force for the Niners. He led the NFC with 17 sacks in 1983 and set an NFL record by recording six in one game.
He would then go on to help the 49ers win two Super Bowls.
He had a sack in Super Bowl XVI against the Cincinnati Bengals and three years later, helped his former Chargers teammates smash the Miami Dolphins in Super Bowl XIX.
Trading away Dean still ranks as one of the biggest mistakes ever made by the Chargers organization.