When you don a player's jersey, you are expressing your respect for him as a player and a person, but you're also saying something about yourself. If you choose to wear #21, you are making a safe choice that no one is likely to question or disagree with. You are expressing your commitment to morality, family values, clean living, and helping your neighbor. If you are taking a child to a ball game (and if you're wearing Casey's jersey, you almost certainly are), you could instruct them, if they get lost, to find someone wearing 21 to help them.
If you are a dude wearing a Casey jersey, you are in the minority. You will probably tuck the jersey into your khaki or denim shorts and wear a belt.
If you are a lady wearing a Casey jersey, you are saying that you're a responsible mom who wants to make the world a better place for her children. You are idealistic about your role as a parent and you're willing to put in the extra effort to make sure that your little darling gets to piano recitals on time, soccer games with an extra bottle of Gatorade, and plenty of quality time with you at the baseball game. You also may have taken a gay man to the prom.