The San Fierro Packers are a fictional professional baseball team based in San Fierro making it the second sports franchise in San Fierro after the 69ers, and one of three known baseball teams in San Andreas (the others being the Las Venturas Bandits and the Los Santos Saints, supposedly forming some sort of rivalry).
Their logo makes a resemblance to their real-life counterpart, the San Francisco Giants. The name can also be a reference to the football team the Green Bay Packers. If so, it's possible the team was originally based in Wisconsin, since the real life San Francisco Giants originally started in New York and shared their name with the New York Giants NFL team.
As the team is sponsered by Fierro Fudge, it can be assumed that the name is a reference to fudge packer, a derogatory term for a homosexual.
In Grand Theft Auto: IV, civilians walking in Beechwood City and Dukes Boulevard can be seen wearing Packers gear, and there is one player's name that appears on the back of the shirt. His name is LaVergne.