The Hammer Hero achievement is worth 15G and is unlocked by throwing the hammer over 86.80m.

The hammer requires good rhythm to achieve maximum power. You are required to keep the blue ball, within the middle of the orange segment. The smoother you are, the more you can consistently keep the ball within the middle of the segment. To break the distance required you dont have to fill meter completely, at least an inch short will probably be enough. Time your throw so the arrow is dead centre, otherwise your throw maybe liable to go foul, or be thrown with too much height or not enough.