Only a team in racing category

What can i do if only a team in a racing category? Must i leave it? Urgent

Well if you want to race and have fun also race with other teams then leaving and joining a fuller league is the only solution.

Okay, but can i still racing only myself?

I suppose, at least you'll win ;-) 

You need at least 2 teams in a tier to have a race. I believe this is to stop people from levelling up while being inactive. And even if you wanted to do that you would level up faster and gain more racing experience in an active league!