Leg bye

A Leg bye occurs if a fair delivery first hits the striker anywhere other than on the bat and does not subsequently hit the bat and results in a run or runs being taken. Sometimes the ball will travel far enough to cross the boundary, in which event 4 Leg byes are scored.
For Leg byes to be awarded the umpire has to be satisfied that the striker was either genuinely attempting to hit the ball with the bat or was hit by it while trying to avoid it - Leg byes should not be awarded if the striker just permits the ball to hit him in the hope that any ricochet will result in a chance to run.
If the batsmen run but the umpire decides that Leg byes should not be awarded he should call and signal Dead ball as soon as the first run is completed, then send the batsmen back to their original ends and disallow any runs scored. Both batsmen are, of course, vulnerable to being Run out while running a Leg bye, even if the Leg bye is itself subsequently disallowed.
Leg byes are not credited to the striker - since he didn't strike them - but to the batting side's total under extras. Any runs scored in this way, but off a No ball, are recorded as No balls, not Leg byes and will be debited against the bowler's analysis, too.