It isn't possible to add extra 'custom' fields to a club's member database.
There is however a workaround by utilising the Messaging Groups functionality.
By creating appropriately named groups via Admin>Set Up>Messaging Groups, and then adding the relevant people to those you can effectively create new fields that can be used by any of your club's main administrators
For example you want to have a role of Coach for some people. It isn’t easy for Play-Cricket to set up extra roles, but by simply adding a messaging group with that title and adding the relevant records from your member database to that group, that is effectively what you have.