When Abbie is telling Ichabod what baseball means to her, one of the things she mentions is that the rules never change. This is false, as even though the overall game is largely the same as when it was first conceived, some minor rules have changed slightly a few times over the years.
In the flashback, Ichabod is present at the hanging of 3 individuals. At the gallows, a lever is pulled and the floor falls away. Depending upon the length of the drop, that hanging method is known as either the standard or long drop. Both were "invented" in the 1860s, long after Ichabod lived.
Standard hanging in Ichabod's time was to have the person stand on something (stool, chair, ladder, horse cart, ...) and simply remove it. The convicted slowly dies of strangulation.
When Abbie threatens the armed Freemasons, she says she'll "call in the damn cavalry," but she pronounces it "Calvary," which refers not to police backup, but to the hill where Christians believe Christ was crucified.