[greymule]

This play happens a lot in girls' FP. I called interference once on a runner who stopped to avoid a squibbed "pool cue" type of grounder and then started again when the ball changed direction and came right at her. She then ran right in front of the fielder (no contact), so it looked bad, but I'll admit I blew it. Both her coaches knew the game well, and in a rather calm post-game discussion, I decided they were right. (I was relieved that her team won the 1-run game, too.)

I would not call interference unless I believed the runner intentionally tried to block fielder's vision. If she runs normally to the next base, she's OK unless there's contact.

In men's SP, it would have to be a blatant attempt to interfere. Just standing in front of the ball and then running as it approached, that's part of the game to me, although some umps will call that.

I've seen umps (wrongly) call interference simply because the fielder shied away from a runner who was doing nothing more than advancing. Unfortunately, the "baseball instinct" to go for the ball aggressively and let the runner hit you for obvious interference is just not there in many players, so we see a lot of troublesome plays.