I was looking at a satallite photo of my old high-school in UK. The school playing field has a number of grids made up of squaree areas. I guess each square is about 10m accross. One grid is made up of 7 by 5 square, another by 6 by 4. Does anyone have any idea what they are used for: cosmic bingo maybe…
I suspect the diamonds are for the game of rounders.
Link showing grids…
Good question.
I see the rounders pitch… the grids… lacrosse, maybe?
I see the rugby pitch. 
Until somebody comes along with a better answer, I’ll propose that the grids are for playing touch rugby. It would be pretty convenient to be able to set and change the size (width) of the pitch based on how many people were playing.
I recall using grids such as this for all sorts of exercises related to team games. It made it easy to have a dribbling competition along a 20-yd section of two adjacent lines, or to be able to keep track of rugby passes to spot forward ones, and so on. They also could be divided up into impromptu 5-a-side pitches.