You want to use setVelocity. If you want to launch them backwards, you could start with the player's direction vector and modify it to get the effect you want (e.g. Invert it, set y component, multiply by desired speed, etc)
This is to 'leap' a player forward into the air, not sure how you'd do it backwards but this may help; Code:java Vector velocity = p.getLocation().getDirection();velocity.add(new Vector(0, 0.4, 0));p.setVelocity(velocity);
Something like Code: Vector velocity = player.getLocation().getDirection(); velocity.multiply(-1).setY(1); player.setVelocity(velocity); You'll have to play with it and experiment to get the effect you want, but that ought to be the general idea.