The game is to be played by players who are on their feet.

"The game is to be played by players who are on their feet".  You will find this phrase, or variations of it, throughout the "Laws of the Game" and it seems, on the face of it, to be a pretty obvious statement.  The confusion comes from the often ignored statement that "players who are off their feet are out of the game".

Let's look at a couple of definitions, because The Rugby Ref likes to be sure we are all talking about the same thing.

Player on his feet:  This is a player whose weight is solely supported on his feet

Player off his feet:  This is a player who is on the ground.  On the ground includes having one knee on the ground, leaning on the ground, or sitting on the ground.  It also includes leaning on, or sitting on, another player who is on the ground.  In other words a player whose weight is not solely supported by his feet.

So if you are off your feet you are out of the game.  The Rugby Ref knows this, but sometimes he sees the players forget it. 

For instance if the ball is made available after a tackle The Rugby Ref often sees players on their knees pick it up and pass it.  The Rugby Ref also sees players lying on the floor sweep it back with their arms.  "But Ref" they cry "it was out" or "you didn't call ruck".  The Rugby Ref then has to remind them that they were off their feet and out of the game.

Sometimes The Rugby Ref sees a player lying on the floor, who tackles the ball carrier.  Most player know this is illegal, what they find harder to comprehend is a player on one knee, or leaning on a player on the ground, who does the same thing.  Remember the definitions.

Finally an example that always has the crowd calling for The Rugby Ref's head.  A player gets tackled close to the goal line and then scrabbles along the floor on his hands and knees to reach out and score a try.  The main reason this causes howls of protest when The Rugby Ref gives a penalty against the ball carrier, is because people have partial knowledge of Law 22.4 (d) and (e).

(d) Momentum try. If an attacking player with the ball is tackled short of the goal line but the
player’s momentum carries the player in a continuous movement along the ground into the
opponents’ in-goal, and the player is first to ground the ball, a try is scored.

(e) Tackled near the goal line. If a player is tackled near to the opponents’ goal line so that
this player can immediately reach out and ground the ball on or over the goal line, a try is
scored.

Either the player's momentum carries him over the line in "one continuous movement", or the player reaches out and grounds the ball "immediately".  What the law does not allow the player to do is fall short of the line and then have another go by doing a baby crawl over the line.

So The Rugby Ref says remember two things:

1. "The game is to be played by players who are on their feet".
2. "Players who are off their feet are out of the game".