Laws of Cricket 1947 Code - Law 20
Before the toss for innings the Umpires shall agree with both sides on the Boundaries for play, and on the allowances to be made for them. An Umpire shall call or signal "Boundary" whenever, in his opinion, a ball in play hits, crosses or is carried over the Boundary. The runs completed at the instant the ball reaches the Boundary shall count only should they exceed the allowance, but if the "Boundary" results from an overthrow or from the wilful act of a fieldsman, any runs already made and the allowance shall be added to the score.
Notes on Law 20
1. In deciding on the allowances to be made for boundaries the umpires will be guided by the prevailing custom of the ground.
2. It is a "Boundary" if the ball touches any boundary line or if a fieldsman with ball in hand grounds any part of his person on or over that line. A fieldsman, however, standing within the playing area may lean against or touch a boundary fence in fielding a ball (see also Law 35 Note 5).
3. An obstacle, or person, within the playing area is not regarded as a boundary unless so arranged by the umpires. The umpire is not a boundary, but sight screens within the playing area shall be so regarded.
4. The customary allowance for a boundary is 4 runs, but it is usual to allow 6 runs for all hits pitching over and clear of the boundary line or fence (even though the ball has been previously touched by a fieldsman). It is not usual to allow 6 runs when a ball hits a sight screen full pitch, if the latter is on or inside the boundary.
5. In the case of a boundary resulting from either an overthrow or the wilful act of a fieldsman, the run in progress counts provided that the batsmen have crossed at the instant of the throw or act.
6. The umpires signals "Boundary" by waving an arm from side to side, or a boundary "6" by raising both arms above the head.
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