This is a modification of the Infantry animation set. I've added the second pikeman melee combat animations to the set, resulting in Infantrymen who, when attack in close combat, will fight back by hitting the enemy with their riflebutt.
No extra files or modifications are needed as long as the directory structure is unchanged. The Infantry_fx.nif is just a copy of the Infantry.nif, therefore it can be deleted if the CIV4ArtDefines_Unit.xml is changed accordingly.
If the Infantrymen also should engage in close combat when fighting range units, the bActAsRanged entry of the Infantry should be changed to <bActAsRanged>0</bActAsRanged>. However, this way the only time when the Infantry shoot will be when they do a first strike.
See also my similar modification for the Rifleman here.
Forum link: http://forums.civfanatics.com/showthread.php?t=355134
Gagonite for his tutorial 'Modifying the Visibilty of Weapons' that also covers how to add other units animations to a unit.
The Coyote for his tutorial 'How to: make minor changes to existing animation without 3Ds max' that contained the information about the necessity of the right node-flag.
Infantry with Melee Combat Animations 2016-10-05
Infantry with Melee Combat Animations