The Oakland Athletics may not be in the National League, but due to the inception of interleague play in 1997 (yes, this travesty has been going on that long!), and due to the fact that Major League Baseball has designated the Giants and the Athletics as “geographical rivals,” the two teams play a home-and-home series each season. So it should be no problem to find Athletics hitters who have had at least 100 at-bats against the Giants, and to see whom among them has had the most success against the Giants.
Jason Giambi had the highest OPS versus the Giants. From 1997-2001 (and briefly in 2009), in 124 plate appearances, he went .262/.339/.523, for an OPS of .862. Unlike any of the other teams at which we’ve looked so far, no Athletic with a minimum of 100 at-bats against the Giants has a higher OPS against them than his total OPS as an Athletic. For example, Giambi’s .862 OPS against the Giants is significantly lower than his .966 OPS as an Athletic against all opponents. Only five Athletics — names we would expect — have at least 100 at-bats against the Giants, and all did worse against the Giants than against all their opponents as a whole. Again, I find this sort of stuff fascinating.
The complete Athletics list, five players long, is here.