There are two circumstances here;
1. A player who has used the new registration system to register twice
As soon as a new user starts registering for a club they will create and claim a player profile. This means we can track the player and ensure they are not duplicated if added to a club again. These users will not be able to register to the same club multiple times and they will receive a message informing them they have already registered for this club.
2. A player created manually by the club who has NOT claimed their profile and uses the new registration system
If a player already exists in a club(having been created by the club manually and not yet claimed) and they register again using the new system a duplicate player will created in your club. To avoid this the best practice recommended is to add email addresses to all of your players before opening registrations. This means you can use the "Alert club via email" option upon opening registrations so that rather than creating a duplicate, these players can simply confirm their registration via the email sent.
Note: If you do end up with any duplicates in your club the CricHQ Support team can help. As a club administrator, email in the duplicates you have found to firstname.lastname@example.org and a member of the team can merge these profiles to collate their stats and information.