I like the tilted lines of concrete block in the back - emphasizes the serendipity of the capture, like what you catch in a quick glance, where you don't know the significance of what you saw until the next moment, but then it's gone.
Although this don't exactly fit the challenge, it's an interesting composition because of the differing elements, and the way the flags connect them. The squares on the wall and the flags seem to connect as well. Cool find.