Examples of Sabaki
From a game between Jowa (White) and Hattori Rittetsu. According to Hashimoto Utaro, - is an instructive example of Jowa's cleverness at sabaki. White can sacrifice and play the vital point a in sente if Black tries to undercut the white group.
Velobici: Could someone add an example of the possible Black undercut of the White group and then supplement that with how prevents the undercut from succeeding.
HookAndLoop: My understand is that a Black play at 'x' is the undercut being referred to. is then atari on Black's atari at 'x'. Black then has to capture and white can fix it's shape in gote.
Suppose white just plays . Now when black decends to white blocks at to keep some eyespace for her group, but since black doesn't have to respond to , he gets another move. In other words, is forcing, but is not. In the sabaki example, a move by black at x is forcing, but white's reply at a is also forcing. This sacrifice to gain tempo? is a standard technique. For additional information see this example and chapter 10 of Tesuji by James Davies.