A batsman scoring 50 (a 'half century') or 100 runs (a 'century', 'hundred' or 'ton'), or any higher multiple of 50 runs, is considered a particular achievement. By extension, a partnership of two batsmen moving the team score on by a multiple of 50 runs, or the team score passing a multiple of 50 runs, is also cause for celebration.
The rules concerning the scoring of runs are mostly contained in Law 18 of the Laws of cricket. The simplest way for a batsman to score a run is by the striker hitting the ball such that both batsmen can run from one end of the pitch to the other without either batsman getting out: the batsmen effectively exchanging positions, so the striking batsman becomes the non-striker, and vice versa. The batsmen may be able to run up and down the pitch more than once, crossing each time, to score two, three or more runs. A batsman can also score four or six runs by hitting the ball to or over the boundary (four if it strikes the ground before the boundary; six if it crosses the boundary in the air without striking the ground), and may be awarded five penalty runs in certain situations. A batsman is never compelled to run (cricket has no equivalent of baseball's force out).
Thus, according to Law 18, a run is scored when:
- the batsmen, or their runner, at any time while the ball is in play, have crossed and made good their ground from end to end;
- a boundary is scored;
- penalty runs are awarded;
- "lost ball" is called.
To score a run, each batsman must run from the popping crease at one end to the popping crease at the other end. A run is "short" if one of the running batsmen fails to make good his ground on turning for a further run (that is, the batsman fails to complete the run by putting some part of his body or his bat on the ground behind the popping crease) – in this event, the number of runs achieved is decreased by the number of "short" runs. Although a short run also shortens the next run, since the second run starts somewhat closer to the destination than it should, the second run is not regarded as "short" if it is completed. A batsman taking up his batting stance in front of his crease may also run from that point without penalty.
If either umpire considers that either or both batsmen deliberately run short, the umpire can give a warning to the batsman that this is unfair and disallow any earned runs from that delivery. If an umpire considers that any batsman deliberately runs short again in that innings, a 5-run penalty is conceded to the bowling side. In practice, this rule is rarely invoked. Also, if either of the batsmen is not in possession of their bat, the run is called short.