Just my take going by the article:
They say he had worn 5 or 6 other different colored pairs of shoes before, so that says something right there. It seems to me that the pink shoes were worn to draw attention to himself, then when they were finally fed up with what he was doing, he began using the grandmother "Breast Cancer Awareness" excuse to conceal his real reason for choosing such a color to begin with. The fact that his coaches ridiculed him about it previously (which I'll assume was more of a warning than insult) and that he insisted on wearing them once again regardless shows that he disobeyed his coaches and was practically asking to be suspended or kicked off the team.

I don't think there's anything wrong with wearing a different color of shoe myself, and to raise awareness of breast cancer with the color pink is an honorable deed, but if you disobey your coaches and must follow rules they've laid out for you, you can't expect to keep everything in place by breaking those rules.