Baseball teams need to stand out from their opponents, the team jersey is an important part of the uniform that helps to do just that. For younger players and those playing recreationally, this might be a t-shirt with your team name on the front and your number on the back. For more competitive or professional teams, this is typically a polyester button up shirt, with your name, team name, logo, and player number. After a couple slides and dives, jerseys will get some new designs in the form of grass and dirt stains. Jerseys are often required in more formal games, but for pickup games whatever you have on should be fine.