The One Inch Punch is a melee upgrade that replaces the player's standard knife in the Zombies map Origins. It allows the player to punch zombies with a powerful force, causing zombies to fly away, similarly to the Thundergun. It can kill a zombie with a single melee attack until round 19.
In order to obtain it, the player must charge up four chests that are located throughout the map (listed below) by killing 30 zombies near them. If a Giant Robot steps on a chest while it's not yet full, it will be reset, and the players will have to kill more zombies. In addition, zombies spawned by a dig spot will not count towards the 30 zombies required to fill the chests. Once completed, players can go to a Rituals of the Ancients station and they will be rewarded with the One Inch Punch, in the form of a glowing energy ball.
Should a player bleed out and lose their One Inch Punch, or otherwise not be present in game when the chests are completed and the Punch is unlocked, the player in question must simply go to a Ritual of the Ancients station, highlight their crosshair over the bottom-most medal, and press the action button. The Punch will then be re-obtainable for the player.
Three of the four footprints containing the chests are located along Odin's patrol route down the center of the map, and the fourth one is found in Freya's path down the western side of the map. The locations from north to south (the direction of all the robots' patrols) are as follows:
The first box is located in the footprint just west of Generator 5 and the Stamin-Up machine, which is stepped on by Odin's right foot. Because this box is the northernmost footprint, it will be the first one that Odin steps on.
The second box is located just east of the Church, or west of the Excavation site, and it is stepped on by Freya's left foot. It is the only one not in Odin's path.
The third box is located in the footprint just east of the Excavation Site and is stepped on by Odin's left foot.
The fourth box is located just west of Generator 4 and the Juggernog machine and is stepped on by Odin's right foot.
The One Inch Punch can be upgraded during the Little Lost Girl easter egg, after hitting roughly 20 Crusader Zombies with glowing arms in the staff room of The Excavation Site with the One Inch Punch. To gain kills toward the Iron Fists, the actual kill does not have to be from the One Inch Punch. Hitting a Crusader Zombie once will cause it lose the glow on their arms, and this counts toward the reward. After reaching the amount, a power-up resembling a stone for the G-Strike will be dropped. It gains a one hit kill attack until round 36 and has an extra elemental attack depending on which staff the player was holding at the time of the pickup; for example, players with the Fire Staff will set zombies on fire with their punches.
The One Inch Punch is a reference to a martial exercise move of the same name in which a person is knocked back several feet from a punch only one inch away popularized by actor and martial artist Bruce Lee.
When upgraded to the Iron Fists, if the player punches a glowing Templar Zombie with it, they will stop glowing.