When the wind comes across the boats on opposite sides, the boat with the wind on the left (port) side, must give way to the boat with the wind on the right (starboard) side. When the wind comes across the boats on the same side and they are not overlapped, the boat behind (clear astern) must keep clear of the boat (clear) ahead. When the wind comes across the boats on the same side and they are overlapped, the boat on the windward (upwind) side must keep clear of the other leeward (downwind) boat. Umpires follow each race and make instant penalty decisions. A green and white flag means no penalty, but a yellow or blue flag means the boat in the match with the corresponding flag flying on the back of their boat must take a penalty before finishing the race. A penalty turn when sailing towards the wind means turning the stern of the boat through the wind and when sailing away from the wind a penalty is taken when the boat turns the bow through the wind. Go to Appendix C of the ISAF’s Racing Rules of Sailing to read the rules for match racing.
*Visit Apenndix C of the ISAF Racing Rules of Sailing to see the match race rules analytically: http://www.sailing.org/tools/