foul or no call

[xxssmen]

I know that the ball is consider part of the hand when the ball is in contact with the hand , so my question is why is it that alot of refs call a foul when players atempt to block a shot and hits the players hand when the ball is still in contact with the hand. I have partners who call this a foul and do I call it the same if my p calls it or let it go?