Coaching the coach...

[IRISHMAFIA]

No, no, no. this is just too big a door to not walk through.

Let the coach keep coming, don't say a word, just smile.

When she reaches you, simply ask, "What's the problem, coach?"

If she just says THE runner left early, simply tell her that neither of your runners moved. When, or if, she specifies R1 left early, tell her, "didn't see that runner leave early coach." Guarantee she'll ask how you could possibly miss it and you will tell her, "Coach, my responsibility is the two trailing runners."

I'm almost willing to bet instead of just turning to your partner, she would ask who's responsibility it is.