Adding Value To A Field When Condition Is Met

I need for a valued to be changed in a row after it checks for how many rows have another value, counting how many and that number making it the amount field.

Example:
Fields- Name sponsor amount

I want access to show how many people have been sponsored by Gabriel... So if 3 where sponsored by Gabriel show 3 to the amount field for Gabriel row! Any way to do this or an easier way?

I for it to check it every time a user is added incase the user added is sponsored by Gabriel add it automatically!