you create a heavy hacky sack that you launch at a creature, then after the spell hits the creature they make a strength DC of 5 if they succeed the spell come's return's to you then you make a DC of 6 after you succeed  the spell launches at your opponent they make a DC of 7 if they succeed the spell launches back at you. After the spell comes back to you you make a DC 8 after you make the strength DC check the spell returns to the target and they make a strength DC 9 following the curve the strength DC increases by 1 after each save.

the damage of the spell is 1d8 after each save the amount of dice used is increase by 1 for example (after the first save it becomes 2d8 after the second it becomes 3d8 and so on)