Here's the rules for a fair catch,if you look at rule c you'll get your answer.
. A fair catch
A catch shall be considered to have been fairly made if(a) throughout the act of making the catch(i) any fielder in contact with the ball is within the field of play. See 4 below.(ii) the ball is at no time in contact with any object grounded beyond the boundary.The act of making the catch shall start from the time when the ball in flight comes into contact with some part of a fielder’s person other than a protective helmet, and shall end when a fielder obtains complete control both over the ball and over his own movement.(b) the ball is hugged to the body of the catcher or accidentally lodges in his clothing or, in the case of the 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. See Law 23 (Dead ball).(c) the ball does not touch the ground even though the hand holding it does so in effecting the catch.(d) 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 first being struck.(e) 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 the ball has previously touched a protective helmet worn by a fielder. The ball will then remain in play.(f) a fielder catches the ball in the air after it has crossed the boundary provided that(i) he has no part of his person touching or grounded beyond the boundary at any time while he is contact with the ball.(ii) the ball has not been grounded beyond the boundary. See Law 19.3 (Scoring a boundary).Note also Law 19.4 (Ball beyond the boundary)(g) the ball is caught off an obstruction within the boundary provided the obstruction had not been designated a boundary by the umpires before the toss
