Measure the length of the wall. This is important because you want to make sure that your football field is symmetric. If your wall is 35 feet in length, for example, you'll need to draw your field appropriately so that your yardage is equal throughout the field. You don't want the left side of your field to be bigger than the right, after all.
Create the field on paper first. This is the place where you will draw out your field to ensure that the measurements are equal. When doing this, don't forget to draw it to scale. Mark off the footage on the paper appropriately, and don't forget to include the end zones.
Pick out the colors you want to use for the football field. Unless you're a Boise State fan (the Buffaloes play on a blue field), you'll probably want to use green for the grass of your football field. The colors of your end zone will depend on the football teams that you like.
Draw the football field in pencil on your wall before you begin painting. This will act as your stencil when you begin painting. By marking your wall in pencil, you can help to prevent painting the football field unevenly on the wall.
Use tape to block off the yard markers every 10 yards on the football field. Painting all of the hash marks of the football field is an unrealistic goal. Instead, paint hash marks for every 10 yards. The tape will allow you to paint the green of the football field first and then fill in the yard markers later.
Paint the end zones after you have finished the football field. Once the green has been put on the walls, you will be able to see exactly how much room you have left for the end zones. This will make painting them a much easier task.