Green is right-of-way boat for Red and Blue and therefore obstruction.
When Red establish an overlap, right of way changes. Rule
11 requires Blue to keep clear.
Rule 15 and because of changing course rule
16.1 requires Red to give Blue room to keep clear. From the time the overlap
begins Blue is unable to give Red room to pass safely between Blue and Green.
Therefore Red is not entitled to room to
pass between Blue and Green (See last part of rule
19.2(b)).