Hi,
One way of doing this would be the following:
in your goal, have a dummy gameObject that always look at the ball. Extract from this its direction ( the looking direction) and normalize that direction, it will give you a vector that represent the direction form the goal to the ball. and because it's normalized it's easy to work with now:
1: get the ball position
2: add to this ball position the goal/ball direction computed above, multiplied by the distance you want from the ball ( say 2)
in effect, this will give you the position of the player, it will be 2 unit before the ball, straight aligned with the goal ( like your picture)
does that make sense?
bye,
Jean