How does one read the actual charts? Some symbols are clearly shots on goal, but others seem like tackles or potentially passes. There also is some kind of shorthand with o's, x's, and the odd hat symbol or a square. I'm curious if there is a standard way of charting a game, or if the author just made up their own shorthand.

Even without knowing how to interpret the chart, you can still see patterns emerge like more action on the sides than the midfield which is pretty interesting.