2. Wrist and elbow issues, especially if people try to hold a fast pace.
3. Low back and spine issues. People may have the tendency to curve their spine when doing this.
I'm not sure legs are stretched much with this exercise; I would say it's mostly strengthening the legs. To stretch any muscle, we need to hold a pose for at least 30 seconds.
Every exercise carries some risk. There are high-risk exercises (running, jogging) and low-risk exercises (power walking, swimming). With this "crawling" exercise, I would put it in the high-risk category.