In order for a unit to charge, the target must be in the hex directly in front of the charging unit (disregarding torso twists) at the beginning of the Physical Attack Phase. The charging unit may not make any weapon attacks in the same turn.
Charging attacks must be declared during the Movement Phase (Ground), but like all other physical attacks, they are resolved during the Physical Attack Phase. This means the charging unit can only attack units that have finished their movement. It also means a charging unit cannot be the target of a charge or death from above attack, because its movement will not be finished until the end of the Physical Attack Phase.
The charging unit must spend MP to enter the target hex regardless of whether or not the charge is successful. If a unit does not have enough MP in the Movement Phase (Ground) to enter the target hex, it may not make a charging attack.
If the attacking 'Mech takes damage during the Weapon Attack Phase that forces the warrior to make a Piloting Skill Roll, the player should roll as normal. A failed roll means the attack automatically misses. Resolve the fall normally at the end of the Weapon Attack Phase. An exception occurs if the unit falls into a paved hex, in which case it is treated as a skidding 'Mech (this is resolved at the end of the Weapon Attack Phase). It will skid for a number of hexes equal to half the hexes it entered during the Movement Phase; when it skids into the hex containing the unit it was attempting to charge, it makes an unintentional charging attack.
If the target takes damage during the Weapon Attack Phase that requires a Piloting Skill Roll and the roll fails, resulting in a fall, the charge attack cannot be made.
MP Loss: A charging unit that loses MP due to damage can still make a charging attack that turn.
Multiple Attacks: A unit may only be the target of one charging or death from above attack in a given turn.
Prohibited Terrain: If the target unit occupies prohibited terrain for the attacking unit, the attacker cannot charge (meaning the player cannot declare a charge attack during the Movement Phase).
Unusual Targets: A vehicle or 'Mech may charge a building hex, or may be forced to accidentally charge a building or hill hex under certain circumstances.
Infantry: Infantry units may not charge or be the target of standard charge attacks.
ProtoMechs: ProtoMechs cannot be targets of charging attacks.
Vehicles: All vehicles except VTOLs, WiGEs, Airships and Fixed-Wing Support Vehicles may make charging attacks. Vehicles may charge other vehicles, but may not be charged by 'Mechs.
Damage
If the attack succeeds, both units take damage from the collision. The defender takes 1 point of damage for every 10 tons that the charging unit weighs, multiplied by the number of hexes moved by the attacker in the Movement Phase, rounding fractions up (the hexes moved do not count the hex containing the target).
The charging unit takes 1 point of damage for every 10 tons the target weighs (round fractions up).
Divide the damage from charging attacks into 5-point Damage Value groupings. The attacking player rolls once on the appropriate Hit Location Table for each grouping.
If a unit charges a target in a building hex, the building hex absorbs damage as normal. The charging warrior also must make a Piloting/Driving Skill Roll modified by +3 in addition to the building modifier to avoid taking damage from entering the building hex. If the charging unit crashes through multiple building hexes, the warrior must make all appropriate Piloting/Driving Skill Rolls upon entering each building hex.
Vehicles: When a vehicle charges a standing 'Mech, allocate damage according to the 'Mech Kick Location Table. Against another vehicle or a prone 'Mech, the normal hit location rules apply. Regardless of whether a vehicle executes a successful charge or is the target of a successful charge, in addition to any rolls that might occur due to damage, the vehicle must make an immediate roll on the Motive System Damage Table.
Unusual Targets: If a charge attack is made against a target with no tonnage, such as a building or hill (for example, as the result of a skid), calculate damage to the attacker using the attacker’s tonnage rather than the target’s.
Location after attack If the charging attack succeeds, the target unit must move as if it had been pushed, and the attacker advances into the target’s hex. If the attacker misses the target, the attacking player places his unit in the hex to the right or left of the attacker’s forward arc.
Prohibited Terrain: If the hex into which the target unit would be displaced is prohibited terrain, neither the attacker nor the target units move. All other effects occur, however, including any Piloting Skill Rolls to avoid falling.
Falls After any successful charging attack, the attacking and target 'Mechs must make Piloting Skill Rolls modified by +2, plus all other applicable modifiers, or fall in the hex they currently occupy.