By definition, a uniform is the distinctive and identical clothing worn by members of the same organization. In team sports, there are common and acceptable minor variations to uniforms. Some football players like their sleeves cut off at the shoulder, others prefer longer sleeves. Major League Baseball gives players the option of wearing their socks inside or outside their pants. The NHL became the biggest stickler for the in-game dress code when it began enforcing the rule forbidding players from tucking their jersey into their pants a la Wayne Gretzky and Alexander Ovechkin.
None of the aforementioned breaches of uniformity strikes me as offensive, but one that does is the oversized, flat-billed, noticeably askew baseball cap. Rightly or wrongly, it's a look associated with hip hop culture, and rightly or wrongly, hip hop culture is associated with street gang violence. I'm not saying every major league baseball player who wears a flat-billed sideways cap is gang-affiliated. My blond-haired whitebread West Island teenaged sons have adopted the look, and that I'm aware of, they're not involved in running gun battles on the mean streets of Beaconsfield.
Besides the obvious sociological connotations, there's the more fundamental issue of professionalism. At the major league level, you should look like a ballplayer. To my mind that means hat straight and bill curled, and if you insist on being a little bit different, stain that bad boy with some infield dirt and tobacco juice. And while you're at it, take the stickers off the underside of the brim. It's your hat now. Wear it like you own it. And don't make me come over there.