This is a season posted by Roger Connor (1885) in one of my all-time progressives. I'm sure this has to do with the quality of LH pitching he happened to face, compared to the qualities of RH, plus the usual small sample size caveats, but I thought this was pretty staggering.
vs LH: 161 AB, 273/343/360
vs RH: 534 AB, 390/440/494
Other lefties on my team were similar but not as extreme.
Larry Walker: 269/322/503 vL and 323/384/489 vR
Jimmy Barrett 276/360/350 vL and 232/318/293 vR (what?!?!)
Ted Williams 274/387/479 vL and 351/454/507 vR