By pulling your wrist like that youre opening up the joint to a lot of fluid and air.
That POP is all that fluid and air escaping, most likely. It's just like cracking any other knuckle. It's a release. However, since youre overloading it (it seems) it may be more intense than youre used to, causing it to hurt.
Personally, I would invest in some tiger paws, let them help support you, and condition your wrists at home or during free time in the gym with wrist strength and for-arm strength.
Taking a ball of socks and squeezing 100 times a day will begin. When that gets too easy, start using a tennis ball.
By the time that gets too easy, you shouldnt have many wrist problems anymore.
Other than that, there are a few wrist push-ups you can try (which are really hard), as well as some other strength ideas your coach may have.
Asking never hurts anyone
Ryan