Franky, just a little more info for you. The rule is that after the cue ball contacts with a legal object ball, ANY ball on the table must contact a rail to which it was not already frozen. It doesn't have to be the cue ball or the object ball which was struck. Another important point though; In your drawing, you show the cue hitting the one ball. If for example the cue ball stops as you have shown it and the one ball continues on and strikes the two ball, it is still a foul if the two ball was also frozen to the rail. If the two ball is not frozen and the one ball hits it and drives it to the rail, then it is a legal shot.