Bring it to the coach's attention privately. Keeping track of a team kids, he/she probably doesn't notice the bullying. Once they're aware, they can watch for it during practice and discipline the aggressor.
If it's a problem involving several kids, it may be wise for the coach to sit the whole team (maybe parents too) and talk about team unity and let them know that negative comments are unacceptable. Depending on the age of the group, they may need to be very specific about what is ok and what is not ok.
If it is one child bullying one other child, it will probably be hard for the coach to notice all of it, so after going to the coach, it may be necessary to talk to the other child's parent.

Wow . . . I would really consider if this is the right place for your granddaughter. If the coach does not want to deal with obvious bulling (not just bulling but physical contact) and ignore it that is a huge red flag.

It may be best to move on and tell the person in charge exactly why you are leaving.