Umpire Question

[dh898]

Newbie here again. This brings up another question I have as I've been working scrimmages. I started out blowing whistles on runs when I saw the ball down but was told anything inside the hash mark don't do that. OK, that I understand as I'm only to blow it when it comes into my area (assuming I'm a line judge). So, if the umpire rarely blows his whistle then anything inside the hash mark is only blown dead by the referee? Is this correct? (And I'm speaking generally) I'm finding that with this knowledge I'm starting to look elsewhere other than the ball when it is not in my territory. The lightbulb is getting brighter, however, the more I learn the more I find out I don't know.