Illegal Blocking

[Jaysef]

I know that in H.S. everything happening between players that start in the blocking zone, until the ball leaves the blocking zone is pretty much legal...will someone help me with the college and pro calls on below -the- waist blocking?
It seems when I'm watching college games, I see running backs blocking rushing defenders, by dropping down and taking out their legs. Same in pros. Correct me if I'm wrong but this IS an illegal block in High School, right?

Dormant Ump