You'll need relationships that link events to managers. Since a manager can be responsible for many events this appearsto be this relationship:
If an event can have many managers, a different relationship using a join table is needed.
The above relationship can be implemented with:
Manager::__pk_ManagerID = Events::_fk_ManagerID
With this relationship, a portal to events on the Manager layout will only list the events assigned to that manager. Other methods using finds or go to related records can be used as can settings in Manage | Security that prevent a manager from editing (or even keep them from viewing) records not assigned to them.