Runner on second base. Batter hits ground ball toward shortstop. While the shortstop is coming in to field the ball, the runner on second advances in a straight line toward third. The runner and the shortstop collide and the ball rolls into left field. Is the runner out?

Answer: Yes, the runner is out. Note: whether the fielder was "in the baseline" is irrelevant.

Under Official Baseball Rules 7.08 Any runner is out when— (b) He intentionally interferes with a thrown ball; or hinders a fielder attempting to make a play on a batted ball;
Rule 7.08(b) Comment: A runner who is adjudged to have hindered a fielder who is attempting to make a play on a batted ball is out whether it was intentional or not. If, however, the runner has contact with a legally occupied base when he hinders the fielder, he shall not be called out unless, in the umpire’s judgment, such hindrance, whether it occurs on fair or foul territory, is intentional. If the umpire declares the hindrance intentional, the following penalty
shall apply: With less than two out, the umpire shall declare both the runner and batter out. With two out, the umpire shall declare the batter out.

A related rule, regarding a runner being "out of the baseline" is 7.08 Any runner is out when— (a) (1) He runs more than three feet away from his base path to avoid being tagged unless his action is to avoid interference with a fielder fielding a batted ball. A runner’s base path is established when the tag attempt occurs and is a straight line from the runner to the base he is attempting to reach safely