1. Do not paint your face in another ethnicity's color.
2. That does not merely mean no blackface. It also means no redface, translating to Native Americans. Or yellow or white or brown or whatever the color is.
3. Do not use sports as an excuse. People dress up in lots of ridiculous costumes for the sake of sports. People even paint their faces. Painting your face in your team colors is perfectly acceptable, even if those colors just so happen to be black, red, brown, etc. But there are many ways to paint your face that do not evoke images of your idea of someone's skintone.
4. If you must paint your face in the color of another ethnicity, stop and think about how an actual member of that ethnicity might react if they see you in said painted face.
5. If you cannot think about that, don't worry. Someone might actually come along and demonstrate.
6. They will not be happy.
7. They will not want to shake your hand.
8. There will, though, be about half a dozen people wanting to record your reaction for posterity and also laughs.
9. Do not wear said facepaint when a protest against the team logo is underway nearby.