ITB, OC comes to me (as BU) and asks if he can put a sub in for the runner he's going to put on 2B. I say, "sure, but let my partner know about it ". As I'm walking out to my position, I overhear the conversation, and the PU tells OC "you can sub for your runner, but she has to advance one base first"
OC was sure, no problem.
I know I should have intervened...