What’s the easiest way to tell the difference between a dress and a sport shirt?
The lines are a bit blurred and there are exceptions on both sides of the fence, but in general, dress shirts tend to be more conservatively styled and colored since they’re meant for, well, being dressed formally. They tend to have stiffer collars (to withstand things like neckties underneath them and suit jacket lapels on top of them).
Sport shirts get away with more patterns, bigger and bolder patterns, pockets, epaulets, decorative stitching and buttons, button-down collars, etc. Sport shirts can get away with collars that are less stiff.