In those cases where the foot never leaves the ground (foot drag), it can be defined as the phase when all portions of the foot are in forward motion. Initial contact (IC): The point in the gait cycle when the foot initially makes contact with the ground; this represents the beginning of the stance phase. It is suggested that heel strike not be a term used in clinical gait analysis as in many circumstances initial contact is not made with the heel. Suggestion: Should use foot strike. Terminal contact (TC): The point in the gait cycle when the foot leaves the ground: this represents the end of the stance phase or beginning of the swing phase. Also referred to as foot off. Toe-off should not be used in situations where the toe is not the last part of the foot to leave the ground.The drop foot gait cycle requires more exaggerated phases. Drop foot SW: If the foot in motion happens to be the affected foot, there will be greater flexion at the knee to accommodate the inability to dorsiflex. This increase in knee flexion will cause a stair-climbing movement. Drop foot IC: Initial contact of the foot that is in motion will not have normal heel-toe foot strike. Instead, the foot may either slap the ground or the entire foot may be planted on the ground all at once. Drop foot TC: Terminal contact that is observed in patients that have drop foot is quite different.
Sometimes it is not visible and the diagnosis is done by actually hearing the slap. Treated systematically, possible lesion sites causing foot drop include (going from peripheral to central):

Neuromuscular disease;
Peroneal nerve (common, i.e., frequent) —chemical, mechanical, disease;
Sciatic nerve—direct trauma, iatrogenic;
Lumbosacral plexus;
L5 nerve root (common, especially in association with pain in back radiating down leg);
Cauda equina syndrome, which is caused by impingement of the nerve roots within the spinal canal distal to the end of the spinal cord;
Spinal cord (rarely causes isolated foot drop) —poliomyelitis, tumor;
Brain (uncommon, but often overlooked) —stroke, TIA, tumor;
Genetic (as in Charcot-Marie-Tooth Disease and hereditary neuropathy with liability to pressure palsies);
Nonorganic causes, e.g. as part of a functional neurological symptom disorder.If the L5 nerve root is involved, the most common cause is a herniated disc. Other causes of foot drop are diabetes (due to generalized peripheral neuropathy), trauma, motor neuron disease (MND), adverse reaction to a drug or alcohol, and multiple sclerosis. Gait cycle
Drop foot and foot drop are interchangeable terms that describe an abnormal neuromuscular disorder that affects the patients ability to raise their foot at the ankle. Drop foot is further characterized by an inability to point the toes toward the body (dorsiflexion) or move the foot at the ankle inward or outward. Therefore, the normal gait cycle is affected by the drop foot syndrome. The normal gait cycle is as follows:

Swing phase (SW): The period of time when the foot is not in contact with the ground.