Tanks can overrun enemy troops during their move phase. Having some monstrous metal behemoth coming straight at you is unnerving for anybody.
During their movement phase a player can declare that a tank is going to attempt to overrun an enemy unit. If the tank has sufficient movement to get into contact with the unit, the enemy must take a Morale check.
To use Tank Shock declare which enemy unit you are driving at with which of your vehicles, and how fast it is moving. Then measure to see if any models from the unit will be reached by the tank. If the tank reaches the unit take a Morale check.
If they fail the check the unit falls back 2D6" – individual models are allowed to be moved out of the path of the vehicle if they would otherwise end up underneath it. The unit can check to see if it is able to regroup in its own turn as normal – but troops will not be allowed to regroup if there is an enemy unit within 6" (such as the tank that forced them to fall back!).
If a unit is moved over by a tank and it passes its Morale check, individual models can be moved out of the way if they would end up underneath it, but otherwise the unit is unharmed. The troops are assumed to move out of the way and resume their positions as the tank passes. Remember that vehicles cannot move over friendly troops, or over vehicles (or wrecks) from either side.
Diagram: Tank Shock. A vehicle drives at a unit of enemy infantry. The unit fails its Leadership test (shown by a Scatter dice and D6 result) and falls back 2D6" away from the vehicle's direction of travel.