in class today one of our new blue belts was sparring a new guy and had him in several submissions from the guard and the new guy basically hurt himself by defending the wrong way/not tapping. After the roll i talked to the new blue and told him to sweep and controll from the top if he spars a noob again. I told him that he should be able to controll a relatively untrained guy who is his size or smaller from uptop so he can controll the pressure when applying a submission hold. So IN MY HUMBLE OPINION. One should at least be able to gain/maintain positional dominance on somone his size or smaller to qualify for a blue belt. Now if the person did judo/wrestling it's a different story. But if you never grappled before, i think it's a good measuring stick.