Interference and obstruction are similar but opposite.
Interference refers to a violation against the offense. It occurs when an offensive player somehow impedes the defensive player’s ability to make a play on a ball. This usually means a player on the field, but since the rules state “an act by the team at bat,” interference can include coaches and players not in the game.
Obstruction occurs when a fielder, who does not have possession of the ball and not in the act of fielding a ball, blocks or impedes the progress of the runner. Physical contact between the fielder and the runner in not necessary for obstruction to be called.