@Cornonthekopp
I'd never heard the term "ghost leg" before, but Wikipedia suggested it as the English equivalent to あみだくじ. If you look at the blackboard on that page, you can see how it works. I think how they set it up is that someone draws three vertical lines with an arbitrary number of horizontal lines connecting them, which they cover up so no one else can see. Then each team picks a starting point at the top. The horizontal lines are uncovered, and the rule is that each team follows a path down the line, swapping with its neighbor each time it encounters a horizontal line connecting it to another vertical line. Each team follows those rules, with C ending up at the left, A ending up in the middle, and B ending up at the right. The text at the bottom is cut off, but you can see that the first characters of each are ド, バ, and フ, for dodgeball, volleyball, and futsal.
I'd never heard of futsal either. Looks like it's just one of those games physical education teachers are so fond of because they can be used to occupy many students with just a small play area.