The Kettlebell swing is a ballistic exercise to train the posterior chain. The kettlebell is swung from just below the groin to somewhere between the upper abdomen and shoulders, with the arms nearly straight.
The key is effectively thrusting the hips, not bending too much at the knees and sending the weight forward, as opposed to squatting the weight up, or lifting up with the arms.
A correct swing requires an intense contraction of the gluteal, abdominal and latissimus muscles.

COMMON MISTAKES

Too much squatting

Many people turn their kettlebell swings into a quad dominant exercise. Always remember a proper swing has maximal hip flexion and minimum knee flexion. Don’t bend the knees too much but hinge in the hips.

Heels or toes coming of the floor

Make sure when performing swings that your feet remain flat on the floor. Heels, toes and balls of the feet should be connected to the floor at all times.

Arms move up prior the hip extension

Remember that the hips are driving the movement. Extend the hips powerfully prior to moving up the arms. If not, arms and shoulders become too active trying to pull the kettlebell up to the desired height. If this happens, you often see that the bell drops rather than being in line with the arms.

Not maintaining a straight back 

It is crucial to keep your spine neutral throughout the entire movement at all times,  so it’s essential to maintain a straight line from your hips to your head. This means that if your upper body moves down, your head goes down as well and therefore stays in line with the rest. If this is not done correctly, you might hurt your back and/or strain your neck.

No full extension in the hips

As the power comes from the hips, it is important to get a full extension at the hips and knees after swinging the kettlebell upwards. Thinking about standing in a vertical plank position, tall and strong with the abs braced and your butt pinching a rock. Well, not pinching a rock but crushing a rock!