49ers: White dudes heading west to get rich and steal from indigineous peoples.
Giants: offensive to little people
Brewers: enticing white frat boys to get drunk
Yes there are many sports nicknames which are offensive to someone.
Boston Celtics is offensive to the real Celtic people.
Notre Dame Fighting Irish is offensive to the Irish.
Dallas Cowboys is offensive to real cowboys.
Green Bay Packers is offensive to real meat packers.
And all the animal nicknames are offensive to the PETA radicals.
Few actual Irish, Scottish or Welsh descendants on the Celtics and few descendants of Norwegians, Danes and Swedes on the Vikings.