why did chris earn an f in physics

From the text:

Chris was a high achiever in almost everything that caught his fancy. Academically he brought home As with little effort. Only once did he receive a grade lower than B: an F, in high school physics. When he saw the report card, Walt made an appointment with the physics teacher to see what the problem was. “He was a retired air force colonel,” Walt remembers, “an old guy, traditional, pretty rigid. He’d explained at the beginning of the semester that because he had something like two hundred students, lab reports had to be written in a particular format to make grading them a manageable proposition. Chris thought it was a stupid rule and decided to ignore it. He did his lab reports, but not in the correct format, so the teacher gave him an F. After talking with the guy, I came home and told Chris he got the grade he deserved.”