If you're gonna call the morning matches "four-ball," then you can't call the afternoon matches "Foursomes," you should call them "two-ball". There are always gonna be four players playing together on Friday and Saturday, so neither "four-ball," nor "foursomes" makes good sense. Why not call them exactly what they are? All four players are playing their own ball in the morning, and the BEST player's BALL for each pair - wins the hole, so call it "Best Ball". In the afternoon, each pair alternates strokes on ONE BALL, and that is called "Alternate Shot".