Seeing as he named his son essentially "ball and chain", I don't think it took that much to get him out the door.
It's nice to be welcomed to a website with the very first post being a not so subtle attack on Buddha, That's ok because the comment show's it's an attack born of ignorance.
Buddha called his Son Rahula(ball and chain) because at the time the boy was born he new it would be very difficult to leave him due to his love for him, the ball and chain represents his attachment to him and the intense difficulty he had leaving.
He left to do what he had to do, the boy was in good hands as he lived in a palace, Buddha was not seeking for himself alone he was looking to guide people to once he discovered the way.
7 years later he reunited with the son who became Buddha's student and was known as the lucky one, at 18 he to became enlightened.
That's why Buddha left, to receive valuable knowledge for himself and others, sacrifices must be made however sometimes you must be cruel now to be kind later because when they reunited he gave his son more then any father could dream of, enlightenment.
It was not a case being tied down by a ball and chain, the reason for it was not even remotely related to that, it represents the difficulty in breaking free of his sons hold on him through love to go off and find his way to help himself and others later, son included.
That is not my interpretation by the way, just the way it's written when read properly, unless you read the name only and make wild assumptions of coarse.
