Anyone have insight into Plank's slantball? Whether it had movement on it or not? Sounds like it was his pitching motion. From what I read. He was a cross-fire pitcher. Stepping toward first and firing across his body. But what was the slantball akin to. I can only guess a cutter or slider.

Plank was coached by Frank Foreman formerly of the Baltimore Orioles:

The crossfire that made Plank famous was invented by Eddie. Foreman saw him chuck a couple one day and nearly fell on Eddie's neck and wept "Kid" Foreman said "you've got the richest thing in line of a cross-fire the old man ever looked at. Keep at it and your made."
Gettysburg Compiler: September 13, 1911