Using Trapcode's Particular, I'd imagine that the apparent screen-hitting can be achieved by making the particles fly towards camera, then stick to a specific layer placed in the appropriate position. Or they could bounce. You set the type of behaviour in Particular.
what about other typesw of camera hits. if I had text that I wanted to fly into the screen. i was just using trapcodes as a visual of the effect I want to achieve. ive got a guy walking down the street swingin a paint stick around. as he gets closer blobs of paint stop and hit the screen.
You just make something grow larger exponentially (or fly it toward a 3D camera), then make it stop abruptly. It should cover up the subject in the shot, since it is imagined to be between camera and subject.
If you use a 3D camera, make sure everything stops at the same distance from camera if you intend to move the camera after the "sticking" happens. Actually, I might move the objects rather than move the camera. That way, you don't have to deal with parenting the "screen-stuck" stuff to the camera so it doesn't appear to move. Because in reality, if something sticks to a moving camera, it doesn't appear to move any more because it's stuck to the camera.
Maybe add a little shake to it (by hand or with the wiggle expression), or add a little shake to the rest of the stuff in the shot to help "sell" the effect.