You make the call!

[Trojans73]

Had this happen in a HS varsity game last night.

Bases loaded with 1 out. The batter hits a comebacker to the pitcher who throws home to get the force. As the catcher is wheeling to make a throw to 1st, the runner from 3rd slides in and takes out the feet of the catcher, who is then unable to make the throw.

I'm not sure what the intent of the runner was as I was a ways off.(Maybe that doesn't matter)

The plate ump called nothing.(Except the force out)

I might have called interference seeing as how the runner was already declared out and he took away an opportunity from the defense.

Opinions? Facts?