My best guess is that you have this relationship:
Members::__pkMemberID = Events::_fkMemberID
Though your field names may be different.
Set up a relationship that matches to events by both memberID AND also by event type and you can match to the earliest "ping" event.
A calculation field constPing might return the quoted text "Ping" and then a new table occurrence for Events can be linked like this:
Members::__pkMemberID = Events|Ping::_fkMemberID AND
Members::constPint = Events|Ping::EventType
(And instead of a calculation, a text field can be used in place of constPing so that by selecting different values, you match to different event types.)
Instead of adding a new table occurrence, FileMaker 12, can also extract this value using ExecuteSQL by setting up a SQL query that extracts this value.