Is gambling OK? Don't bet it! There's not an easy or instantly obvious proof text answer to that question.
Gambling has been an entertainment ever since, however I think what is considered illegal is a sin, so maybe if you are gambling and it is not legal, it can be considered as a sin. Gambling is really fun, but I think if it is against the law, it's just like committing a sin.
That would be considered as breaking the law not sin, both things are different. Sin is something which is wrong form religious point of view and in many famous religions of the world, this bloody game has been prohibited because it destroys the lives of people who dont have good control over their greed. Thus the involvement of greed makes it sinful act, otherwise it could have been fun for people.