In Interphase, the cell is going through three different things. In G1, the cell is growing. It is also synthesizing which means that it is replicating DNA. During G2, It is prepping for mitosis. The field represents the cell and the band members represent the chromosomes. The band is standing on the sideline prepping for the show to start, this demonstrates how the chromosomes are prepping for mitosis.
In prophase, the chromosomes coil up and become visible. They aren't arranged in any particular way in the cell. The marching band shows this by not being arranged in any way on the field.
In metaphase, the chromosomes line up along the equator of the cell. The band represents this by lining up in the middle of the field.
In anaphase, the centromeres divide. The chromosomes move toward opposite poles. The band shows this, because they are moving toward opposite lines.
In telophase, a nuclear envelope forms around the chromosomes at each pole, and the coil dissolves. The band shows this because the kids are almost at their own "cells".
In cytokinesis, two cells are completely formed. The band shows this by having two distinct groups of woodwinds (on the right) and brass (on the left).