Maybe it's me, because I took it, but I go right to the triangle made by the two people and the ball. And the people are arranged in a triangle.
There are a lot of triangles all the same shape (flat and pointing left or right). The largest area of grass is a prominent triangle. Two smaller areas of grass (considering the tree shadow as not-grass) are also triangular. The long wall of the building and the receding row of shrubs are truncated triangles that complement each other. All these basically horizontal skinny triangles create a relaxed effect, which could go too far, into dead calm, if the numerous small vertical accents weren't there: trees, posts, people, and the upright whatevers on the side of the building. I think the composition works because of these repetitions of shapes.