Question: What If The Ball Goes out of the Arena?...

[AIBob]

Originally Posted by S01

... An example of unsafe operation is repeatedly throwing balls off the field at audience members...

The main difference between the example in S01 and accidentally throwing a single ball into the audience members, is just that, in the example, the robot repeatedly throws balls off the field...
So if you were, say to just have one ball thrown out (throughout the whole event) on accident, then you probably wouldn't get a penalty (through that is up to the head ref).