Q. Why would your 6 month puppy run into your legs while running towards you?
A. I guess your puppy is very energetic and lively and it is hard for him to control his movements completely. It can also depend on the puppy's breed too, I had an English Bulldog who would always do that when exited and happy to see me. It might be worthy to try to train him, if you haven't started it yet, by attending some lessons with a reputable trainer. It will teach him a lot about play time and "work" time, and his manners will improve a lot as well !