The folk law says that in the English town of Rugby, during a soccer match, one young player picked up the ball and started running and all the others tried to catch him.
The game of Rugby Union was born.
The basic idea is that the ball must be passed backwards to a team mate [that is someone standing behind you in relation to the goal line] who then runs forward and passes the ball back etc etc.
In Rugby Union, once you have been tackled to the ground without having been able to pass the ball, you must release the ball backwards by placing in stationary on the ground.
The other team may not [in general circumstances] snatch it away, and one of your own team will pick the ball up and it starts again.
In Rugby League, [a breakaway code that strted in Australia over a dispute about player payment and professional/amature status] the rules are slightly different.
To the casual observer, the main difference will be that once tackled, both teams reset in defensive and attacking lines respectively, and the player who has the ball "plays the ball" by placing it on the ground and quickly rolling it back between his legs to a player known as the "dummy half" who may pick it up and run or pass etc.
The term "dummy half" is not used because he is a "dummy" but rather because his position in waiting for the ball is like a "dummy" or "fake" HALFBACK, which is a player who has the function of waiting for the ball to come out of a "scrum".
Rugby uninion and Rugby league can best be described in relation to one another in the same way that Softball and Baseball have many similarities.