The striker is out Caught if a ball delivered by the bowler, not being a No ball, touches his bat without having previously been in contact with any fielder, and is subsequently held by a fielder as a fair catch, as described in 3 below, before it touches the ground.
2. Caught to take precedence
If the criteria of 1 above are met and the striker is not out Bowled, then he is out Caught, even though a decision against either batsman for another method of dismissal would be justified.
3. A fair catch
Providing that in every case neither (i) at any time the ball nor (ii) throughout the act of making the catch as defined in Law 19.4, any fielder in contact with the ball is, as described in Law 19.3(b), touching the boundary or grounded beyond the boundary, a catch shall be considered to be fair if (a) the ball is hugged to the body of the catcher or accidentally lodges in his clothing or, in the case of a wicket-keeper only, in his pads. However, it is not a fair catch if the ball lodges in a protective helmet worn by a fielder.
(b) the ball does not touch the ground even though the hand holding it does so in effecting the catch.
(c) a fielder catches the ball after it has been lawfully struck more than once by the striker, but only if it has not been grounded since it was first struck.
(d) a fielder catches the ball after it has touched an umpire, another fielder or the other batsman.
However, it is not a fair catch if at any time after having been struck by the bat and before a catch is completed the ball has touched a protective helmet worn by a fielder.
(e) a fielder catches the ball after it has crossed the boundary in the air, provided that after being struck by the bat, the first contact with the ball is by a fielder, not touching or grounded beyond the boundary, who has some part of his person grounded within the boundary or whose final contact with the ground before touching the ball was entirely within the boundary.
Any fielder subsequently touching the ball is not subject to this restriction. See Law 19.4 (Ball beyond the boundary).
(f) the ball is caught off an obstruction within the boundary that has not been designated a boundary by the umpires before the toss.
A catch shall not be made and a Boundary 6 shall be scored if after the ball has been struck by the bat a fielder
(i) has some part of his person touching or grounded beyond the boundary when he catches the ball, or after catching it subsequently touches the boundary or grounds some part of his person beyond the boundary while carrying the ball but before completing the catch as defined in Law 19.4.
(ii) catches the ball after it has crossed the boundary in the air without the conditions in 3(e) above being satisfied.
See Laws 19.3 (Scoring a boundary) and 19.5 (Runs allowed for boundaries).
5. No runs to be scored
If the striker is dismissed Caught, runs from that delivery completed by the batsmen before the completion of the catch shall not be scored but any runs for penalties awarded to either side shall stand. Law 18.12 (Batsman returning to wicket he has left) shall apply from the instant of the completion of the catch.