All changes in velocity from cyclic movements are known as transitions.

Ground Resonance
In flight, most parts of a helicopter vibrate at their own natural frequency. On the ground, they collect through the landing gear - if its natural vibration matches that of the main rotor, every time a blade rotates, the present vibrations receive another reflected pulse to increase their amplitude, and which can cause the aircraft to tip over and be destroyed. Peculiar to some helicopters, with fully articulated rotors, because they have dragging hinges (they are there to counteract vibration caused by movement of the blade's centre of mass), this is indicated by an uncontrollable lateral oscillation increasing rapidly in sympathy with rotor RPM. It could also be caused by blades not being in balance, unequal tyre pressures or finger trouble, but will only occur if the gear is in contact with the ground. It's best avoided by landing or taking off as cleanly as possible, but, if it does occur, you must either lift off or lower the collective and close the throttle.

Dynamic Rollover
This occurs when your helicopter has a tilted thrust vector with respect to the C of G, commonly encountered with some side drift when you have one skid or wheel on the ground acting as a pivot point, but you can also get a problem when your lateral C of G falls outside the width of the skids or wheels. Every object has a static rollover angle, to which it must be tilted for the C of G to be over the roll point, for most helicopters being 30-35°. As your lateral cyclic control at that point is a lot less effective than if you were hovering, because it is not rotating around the C of G, but the rollover point, you have less chance to get out of trouble, and the only effective control is through the collective (do not raise it). In other words, the lift from the rotor disc that should be vertical is inclined and converted into thrust, above the centre of gravity, so trying to use the cyclic to level, and the collective to get you off the ground is wrong!