Chicken is debatable and I can understand why you would think it's not right.

Use one's weight and strength against him is the CORE mechanic of Jiu Jitsu. One Jiu-Jitsuka was a world champion of free-fight for a reason. With this in mind, why one could use a dragon's weight against himself ? Charge its leg, make him fall... Simple. You makes a creature loose its footing and it falls because of that, not because you apply more wheight than he have. Plus, it's not a weight vs weight problem, but a weight with gravity center, and overall balance vs strength applied within this system.