"This strange hammer is one of Kilton's specialties. Being struck by it doesn't hurt much, but the fourth swing in a string of attacks will send the victim flying."
Hyrule Compendium

The Spring-Loaded Hammer is an item in The Legend of Zelda: Breath of the Wild. It is single-handed Hammer designed by the monster researcher Kilton which can be purchased from his Fang and Bone shop at night for 199 Mon, making it one of the few weapons that can be purchased. Though it is the only hammer that can be wielded one-handed and has high durability, it has a base attack power of 1, thus it is not very powerful damage wise. However its 4th swing produces extra knockback that will send enemies flying. However due to its low attack power, it is more of a novelty weapon. However it makes up for it in durability, knockback, and ability to be purchased. The weapon is efficient against Bokoblins or Moblins particularly near a deep enough source of water to drown them. Link can simply knock them into the water for an easy kill.

See also