Why would you measure discipline by any metric other than performance? My high school XC team showed that we were disciplined by having our first ten guys finish before the other team's top runner in dual meets with area teams. We showed that we were disciplined by finishing in the top 5 at states every year I was there. I showed that I was disciplined by being the number one runner on a state champion team. We didn't go around worrying about who was wearing what kind of hair style. We just wanted to fucking win.
Hair style is the kind of thing that a loser pretends is a sign of discipline. People who won't make the effort necessary to prove themselves in competition need to find trivial things to point to to show that they are serious so that they can say "sure I ran a 2:15 800m and the fastest girl in the girls' race ran faster than me, but look at the way I'm dressed! Look at my hair! I'm so disciplined!"
Discipline is proven by performance. Nothing else.