This happened to me earlier in the week. I shampooed (sulfate-free), conditioned, and detangled my hair--I felt tender around the crown of my head for the next two days. I can't understand it because I finger combed to detangle and I wasn't rough with my hair at all.
I've experienced this tenderness from time to time (sometimes this is after detangling--sometimes it isn't). It goes away after a couple of days, but the precise cause confounds me.