Firstly let me say that Yan's knee was 100% illegal under the current rules and Sterling had no reason to expect it. That being said, that knee from Yan should be legal 100%. The grounded opponent rule was created to protect fighters from having their heads smashed against the canvas by knees/stomps ala Mark Coleman vs. Igor Vovchanchyn or Kevin Randleman vs. Kenichi Yamamoto, not to protect them from getting struck in a crouching position. The definition of grounded needs to be changed to refer only to fighters who are on their backs or in a turtle position. Its an outdated rule that does nothing for safety and just limits fighters tools.