In professional baseball, there are no specific rules against wearing a baseball hat backwards. However, many teams and organizations have their own dress codes and uniform policies that may dictate how players can wear their hats.
Some teams may allow players to wear their hats backwards during pre-game warmups or batting practice, but require them to wear them forward during games. Other teams may have more lenient policies that allow players to wear their hats backwards during games or at any time.
It’s important to check with the individual team or organization for specific policies on hat-wearing. In general, however, wearing a baseball hat backwards is a matter of personal preference and style, and may be more common among younger or less traditional players.