Retired runner INT?

[AtlUmpSteve]

Let's go back to the OP.

NFHS interpretations have historically followed ASA (now USA) any time there wasn't a clear rule or case play distinction. In this case, that has meant:

Runners are expected to attempt to advance to be safe at the next base; doing that, and only that, isn't interference. Once put out (and acknowledging they don't immediately disappear in that instant), they are obligated to "not interfere". That means:

If the runner is out and struck by an immediate throw while properly attempting to advance directly to the base, that isn't interference. If the runner veers into a path where struck by the throw, intentionally or NOT ("she was trying to avoid"), that IS interference. A runner that stays up (rather than slide) probably ISN'T trying to advance safely, and could easily be considered interfering.

In these other scenarios, use the "reasonable man" theory. If a runner could have avoided interfering and didn't, that's interference. If a defender would reasonably mistake a retired runner for an active runner, that's interference.
The "runner didn't know" isn't a defense, that's why they have base coaches; once retired, the onus is on the runner to NOT interfere, just like the onus is on the defense to not obstruct.