Obstruction of justice is when someone does something to stop or interfere with a legal investigation or trial. Imagine if you were playing a game with friends and somebody hid one of the pieces you needed to win. They would be obstructing your progress in the game. In the same way, if someone hides evidence, lies to the police, or tells others not to talk to investigators, they are obstructing justice. This is against the law because it makes it harder for the legal system to find out the truth and make sure justice is served. It's like playing a fair game where everyone follows the rules, so that the game can be won fairly.