Do I need to Lock the League Event / Round?
You do not need to Lock an Event / Round once it is completed, but it is good practice. At midnight after the Event / Round is completed it will be automatically locked.
If you Un-Locked an Event / Round to make a change, it is good practice to Lock the event again once the change is made. If you do not Lock the Event / Round, they will be automatically locked that evening at midnight.
To see how to Lock / Unlock an Event refer to the following article Event / Round - Lock & Unlock
To see why Events & Rounds are Locked please refer to the following article Why are Events / Rounds Locked?