We will explain it to u when we ourselves get to know what they stand for. Nordeus thinks we are all Sherlock Holmes and it lets us figure it ourselves

There are many assumption. I and many other feel that the arrows show the mentality of that player as an individual. Blue will be defending and red will be attacking. Some feel that a blue arrowed player will move half a block back like an MC will become half DMC half MC and the red arrow player will move half block ahead. Some believe that the player with blue arrow moves back when his team does not have the possession of the ball and when it has, it remains in his position and red arrowed moves ahead when his team has the possession of the ball and stays in his position when it does not.
It can be either of these or something else. Or maybe they are ornamental and do nothing.... U decide
Nordeus will never tell us