If you would like to group sprints with the name pattern starting with “Scrum” you might slightly adjust the expression.
First, check the CurrnetMember name directly, not its Parent.
When checking on name patterns, use the regular expression .* (see examples in Regular expressions in calculated members).
[Sprint].CurrentMember.Name MATCHES "^Scrum.*"
For more complex use cases to group sprints by name patterns, check out other community posts describing how to create a custom hierarchy in the Sprint dimension.