Those of you who have begun learning and practicing kettlebell swings should already know that you must have a powerful gluteal contraction to perform them correctly. What you may not know is that many people struggle with neurologically recruiting their glutes, because of habitual sitting throughout the day or inactivity. When people cannot preferentially recruit their glutes to perform powerful hip extension, the brain attempts to compensate by firing the hamstrings and back extensors to complete the quick hip drive. If this continues, not only will your kettlebell never swing correctly, but you may cause a lower back injury or chronic lower back pain.
So, start fixing the problem by reteaching your brain to contract your glutes for hip extension. Begin with mastering the Gray Cook Hip Lift, or other glute bridge techniques on the floor.