If a player gave this line as an excuse as to why he just lost the gold-medal round of the Olympics, he would probably be called a very sore loser. However, he would not totally be wrong if he said that.
Gravity does play a large and important role in judo.
It's what makes it possible to throw someone with ease. It's the reason why we are able to pin our opponent to the floor. The heavier your opponent, the larger the gravity that acts on him is. The gravity that acts on him at this point will make him lean or fall. He steps forward towards you to put his right hand on your left lapel.