It isn't possible to add extra 'custom' fields to a club's member database - they would appear for every club, not just your own, and would probably not be relevant to other clubs. The list would just grow and grow until it became unmanageable
There is though, a way of doing this by utilising the Messaging Groups functionality. So 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.
Similarly you might want to indicate if a person has paid (or not paid) their subscription, or is attending the club dinner. Again, add a messaging group and you can add and remove people as necessary.
The number of different roles and fields that individual clubs and leagues require is almost infinite, and a field set up for one site would show on everyone’s; but this method allows you to create the fields that you want in your database without affecting other people’s.