A new rules query came up in a game yesterday and neither my opponent nor I could find a rule for it.
My opponent's Librarian was locked in combat with a unit of 10 infantrymen when a second unit charged him. My opponent then issued a challenge to this second unit.
My thoughts were that this was not permitted as it would make little sense for a character who is already dodging blows to be able to step back and issue such a challenge. It's even less likely that members of the unit with whom he is already fighting would stop, step back and allow him a square go with another unit's Captain!
However, we could find nothing in the BRB that prevented it. Does this sound right to anyone as if it is allowed, it feels like it could be easily abused?