Three boats, the Flying Fifteen (L), the F16 (M), and the Wayfarer (W) are approaching the line to start, all on starboard tack. Initially, W is clear ahead of L and M, and is parked just below the starting line at the signal boat. At this point, L and W are required by RRS 12 "ON THE SAME TACK, NOT OVERLAPPED" to keep clear of her. W is also clear astern of L and is required to keep clear of her too.
L establishes an overlap to leeward of W from clear astern, I presume within two of her boatlengths. Just how far apart they are is not specified. W must now keep clear of L under RRS 11 "ON THE SAME TACK, OVERLAPPED". L must initially give W room to keep clear under RRS 15 "ACQUIRING RIGHT OF WAY". M must still keep clear of both W and L.
M sails in between L and W. Now all three boats are overlapped with each other (see the definition of overlap). W must keep clear of L and M (rule 11). M must keep clear of L (rule 11). M must initially give W room to keep clear (rule 15). RRS 15 does not apply between L and M, so L is not initially obligated to give M room to keep clear. How close the boats are at this point is vitally important, and will probably determine the outcome of a protest hearing.
30 seconds before the starting signal, L heads up. M also heads up, and so does W (to head-to-wind). W crosses the starting line and stops. L must give M room to keep clear under RRS 16.1 "CHANGING COURSE". M must give W room to keep clear also.
After the starting signal, M hails for room. L bears away. L's transom swings towards M. M steers away and makes contact with W. The is no damage.