The level of the beer in the Green Stocking player's mug changes during the pregame prayer invocation.
Several times the Walnut Grove team batted out of order. In the first inning Doc Baker batted ahead of Mr Edwards. In the last inning Doc Baker batted after Mr. Edwards.
The numbers that Laura and Mary write on the board during the game change in appearance between shots.
Despite taking place in 1875/1876, before the Centennial, the pitchers in the game threw overhand. Per the rules, overhand pitching did not start until 1884.
Before the game Sleepy Eye captain argues in favor of the teams getting 4 outs an inning like they did in their previous game. Baseball had been using 3 outs per side for over 20 years by then.
All the players on the Sleepy Eye team are wearing gloves when fielding. The gloves also have webbing which would not be the case until the early 1900's. The episode takes place in around 1880, and at that time only the catcher and first baseman wore gloves. The other fielders would play bare handed. These are some of the many baseball anachronisms made.
Reverend Alden was counting foul balls as strikes. Foul balls didn't start counting as strikes until the National League adopted the rule in 1901. This game takes place more than 20 years before that.
After the game Charles is in bed redoing The Home Mechanic. That book wasn't published until 1903.