The 1903 World Series was the first of baseball’s modern era. Boston and Pittsburgh were adhering to newly codified rules of play — and also initiating a new code of dress, as no one could have known, least of all the men in the stands, uniformly obedient to the laws of Edwardian haberdashery. The spectators wore “derbies, boaters, checkered caps and porkpie hats,” wrote Beverly Chico in her book, “Hats and Headwear Around the World.” Each style signaled a distinct social identity. All are now regarded largely as museum pieces, having fallen away in favor of a hat that offers casual comfort and a comforting image of classlessness. Given our cult of youth, our populist preference for informality and our native inclination toward sportiness, its emergence as the common man’s crown was inevitable.

Frank Sinatra supposedly implored the fedora-wearers of his era to cock their brims: Angles are attitudes. Ballplayers have accepted this as truth since at least that first World Series, when Fred Clarke, Pittsburgh’s left fielder and manager, wore his visor insouciantly askew, and the general public has come to know the ground rules as well. Here’s a test of fluency in the sartorial vernacular of Americans: You can read the tilt of a bill like the cut of a jib. The way you wear your hat is essential to others’ memories of you, and the look of a ball cap’s brim communicates tribal identity more meaningfully than the symbols stitched across its front. Is the bill flatter than an AstroTurf outfield? Curved like the trajectory of a fly ball? Straightforwardly centered? Reversed like that of a catcher in his crouch or a loiterer on his corner? The cap conforms to most any cast of mind.

Watch people fiddling with their baseball caps as they sit at a stoplight or on a bar stool, primping and preening in what must be the most socially acceptable form of self-grooming. No one begrudges their fussiness, because everyone appreciates the attempt to express a point of view. The cap presents studies of plasticity in action and of the individual effort to stake out a singular place on the roster, and the meaning of the logo is as mutable as any other aspect. To wear a New York Yankees cap in the United States is to show support for the team, maybe, or to invest in the hegemony of an imperial city. To wear one abroad — the Yankees model is by far the best-selling Major League Baseball cap in Europe and Asia — is to invest in an idealized America, a phenomenon not unlike pulling on contraband bluejeans in the old Soviet Union.

The New York Knickerbocker Base Ball Club, often acknowledged as the sport’s first organized team, introduced the baseball uniform in 1849: blue wool pantaloons, a white flannel shirt, a broad-brimmed straw hat. The hat had nothing particularly to do with the fight against glare, and the world had not yet brought “branding” upon itself. The Knickerbockers were hatted simply because it was the 1800s, and they were respectable men in a public space.