There are two places where the Auto Refresh functionality can be turned ON or OFF. By default it is ON. See the screenshot below to see this option at the View level:
The next screenshot shows the option at the Report creation page:
Unfortunately there is no global setting for this to be set to OFF by default, however an enhancement request was created (ID 158695) to have an option to disable AutoRefresh in the Admin > Config option.
At this point in time, the highest level you can set this at, is at the view level. If you really needed to, you could stop Yellowfin, then run some queries directly against your YF DB to update the views and set AutoRefresh to off.
update ReportView
Set AutoRefresh = 0
where ViewId = <ViewID>
This means that any NEW reports based on this view will have the AutoRefresh set to off. But the setting will not take affect until you restart YF, and if will not affect existing reports. However, to run a similar query against your existing reports, you will need to run:
Update ReportFormat
set FormatCode = 'MANUAL'
where FormatTypeCode = 'EDITDATAREFRESH'
and ReportId in(<Report IDs>)
This should cover both bases, but as usual, with any DB update, you should ensure you have a recent backup and thoroughly test your most used objects after making these changes, just to be on the safe side.