Should you be able to knee somebody ducking below the waist?

This is one of the illegal things I think that should be illegal. Similar to MMA its illegal to kick somebody in the face when they have 3 points down. In boxing, it's really frustrating to see people duck below the waist sometimes below the knees and people call it slick boxing. In real life if somebody duck below the waist, you'd just shove you knee or shin in their face and they'd be laid out cold.