sorry for the lack of informations, but thank you both for your reply.
i was lying sick in my bed and was so tired and did'nt wrote a good post. sorry for that.
to your questions:
1.) the game is top-down. on the left site player 1 and right player 2
2.) player-behaviour: 8 direction (player 1 moved with WASD)
player 1 is blue, player 2 is orange.
the "ball" is red.
my point is:
how do i make the ball pass trough the slightly transparant green barrier in the middle of the screen, but keep the players away from getting on the oppenents site?
the green barrier can't have the "solid"-behaviour, because the ball can't fly trough it...