This came up the other day in a Etchells start.

The line is set square to the wind which is blowing 5-7 knots.

Two boats, A and B are sailing down the line on Stbd.
A and B are overlapped but B's bow is close enough to A's
transom (overlapped by a two or three feet) to limit
A's ability to head up without hitting B.

There are a series of boats, close hauled on stbd, below B
calling for room.

What's B's responsibility in this situation? Does she have to
slow down or bear off to give A room to head up? If the boats
coming up from below reach B before she has been able to
untangle herself from A, is B in the wrong?