Law 19 (Boundaries)
1. The boundary of the field of play
(a) Before the toss, the umpires shall agree the boundary of the field of play with both captains. The boundary shall if possible be marked along its whole length.

(b) The boundary shall be agreed so that no part of any sight-screen is within the field of play.

(c) An obstacle or person within the field of play shall not be regarded as a boundary unless so decided by the umpires before the toss. See Law 3.4(ii) (To inform captains and scorers).

2. Defining the boundary – boundary marking
(a) Wherever practicable the boundary shall be marked by means of a white line or a rope laid along the ground.

(b) If the boundary is marked by a white line,
(i) the inside edge of the line shall be the boundary edge.
(ii) a flag, post or board used merely to highlight the position of a line marked on the ground must be placed outside the boundary edge and is not itself to be regarded as defining or marking the boundary. Note, however, the provisions of (c) below.

(c) If a solid object is used to mark the boundary, it must have an edge or a line to constitute the boundary edge.
(i) For a rope, which includes any similar object of curved cross section lying on the ground, the boundary edge will be the line formed by the innermost points of the rope along its length.
(ii) For a fence, which includes any similar object in contact with the ground, but with a flat surface projecting above the ground, the boundary edge will be the base line of the fence.

(d) If the boundary edge is not defined as in (b) or (c) above, the umpires and captains must agree, before the toss, what line will be the boundary edge. Where there is no physical marker for a section of boundary, the boundary edge shall be the imaginary straight line joining the two nearest marked points of the boundary edge.

(e) If a solid object used to mark the boundary is disturbed for any reason during play, then if possible it shall be restored to its original position as soon as the ball is dead. If this is not possible, then
(i) if some part of the fence or other marker has come within the field of play, that portion is to be removed from the field of play as soon as the ball is dead.
(ii) the line where the base of the fence or marker originally stood shall define the boundary edge.

3. Scoring a boundary
(a) A boundary shall be scored and signalled by the umpire at the bowler's end whenever, while the ball is in play, in his opinion
(i) the ball touches the boundary, or is grounded beyond the boundary.
(ii) a fielder, with some part of his person in contact with the ball, touches the boundary or has some part of his person grounded beyond the boundary.

(b) The phrases 'touches the boundary' and 'touching the boundary' shall mean contact with
either (i) the boundary edge as defined in 2 above
or (ii) any person or obstacle within the field of play which has been designated a boundary by the umpires before the toss.

(c) The phrase 'grounded beyond the boundary' shall mean contact with
either (i) any part of a line or a solid object marking the boundary, except its boundary edge
or (ii) the ground outside the boundary edge
or (iii) any object in contact with the ground outside the boundary edge.

4. Runs allowed for boundaries
(a) Before the toss, the umpires shall agree with both captains the runs to be allowed for boundaries. In deciding the allowances, the umpires and captains shall be guided by the prevailing custom of the ground.

(b) Unless agreed differently under (a) above, the allowances for boundaries shall be 6 runs if the ball having been struck by the bat pitches beyond the boundary, but otherwise 4 runs. These allowances shall still apply even though the ball has previously touched a fielder. See also (c) below.

(c) The ball shall be regarded as pitching beyond the boundary and 6 runs shall be scored if a fielder
(i) has any part of his person touching the boundary or grounded beyond the boundary when he catches the ball.
(ii) catches the ball and subsequently touches the boundary or grounds some part of his person beyond the boundary while carrying the ball but before completing the catch. See Law 32 (Caught).

5. Runs scored
When a boundary is scored,
(a) the penalty for a No ball or a Wide, if applicable, shall stand, together with any penalties under either of Laws 18.5(b) (Deliberate short runs) or 42 (Fair and unfair play) that apply before the boundary is scored.

(b) the batting side, except in the circumstances of 6 below, shall additionally be awarded whichever is the greater of
(i) the allowance for the boundary.
(ii) the runs completed by the batsmen, together with the run in progress if they have crossed at the instant the boundary is scored.

(c) When the runs in (b)(ii) above exceed the boundary allowance, they shall replace the boundary for the purposes of Law 18.12 (Batsman returning to wicket he has left).

6. Overthrow or wilful act of fielder
If the boundary results either from an overthrow or from the wilful act of a fielder the runs scored shall be
(i) the penalty for a No ball or a Wide, if applicable, together with any penalties under either of Laws 18.5(b) (Deliberate short runs) or 42 (Fair and unfair play) that are applicable before the boundary is scored
and (ii) the allowance for the boundary
and (iii) the runs completed by the batsmen, together with the run in progress if they have crossed at the instant of the throw or act.