Red has fouled Blue. As she tacks, Red is subject to rule 13. After that, Red is
subject to rule 11 and
must keep clear, which she does not do. Blue establishes an inside overlap from
clear astern after Red passes head to wind inside the zone and is subject to
rule 17. Because Blue
is now inside overlaped Red shall give her mark-room (see rule 18.2(a)). Blue may
sail her proper course but not above it. The collision occurs because Red keaps
not clear and does not give mark-room. Therefore Red breaks rule 18.2(a) and rule
11. Rule 18.3 does not apply
because the mark has to be left on starboard.