How is the low back pain after Smith finished squatting? Did this action hurt his back?

Incorrect squats can easily hurt your waist. First of all, as long as the thigh reaches a slightly lower level, don't squat; Secondly, when you do it, you must stand up straight. If your waist is loose, the forward force on the lumbar spine is too great, which will hurt your waist. Also, pay attention to breathing, breathe when you go down, and shout when you come up. This wrong action must be corrected as soon as possible. After a long time, it will strain the lumbar muscle, which is irreversible damage.