Is it normal for my newborn to curl his wrist/hand inwards? sometimes with a hand in a fist sometimes not?

If the infant moves the wrist and hand freely in all directions it is OK

Babies were in a tight spot inside Mom before being born, so they tend to feel comfortable being curled up into a ball during the first few weeks after birth. They are used to being in that position, but will outgrow it and stretch out soon. If worried about movements or positions in a baby, one can just take a video for 20 seconds and show it to the baby's pediatrician.