Explain · Like I'm five version
The offside rule in terms of jumping a queue
The offside rule is just like being told you cannot sneak to the front of the school lunch queue before your friends have arrived with the tray.
When you play football, you must wait for the ball to be passed to you while there are at least two people from the other team between you and the goal. Think of the goal as the place where the delicious chicken nuggets are kept. If you stand right by the kitchen door while your teammate is still way back by the playground gate, the dinner lady will blow her whistle. She says you are offside, which is just her way of saying you are trying to cheat to get your lunch first.
If you are level with the last defender when your friend kicks the ball, you are allowed to run forward. This is like waiting for your best friend to finally reach the front of the line. Once they are there and the path is clear, you can go ahead and grab your food. But if you were already standing there all alone while everyone else was stuck waiting, you have broken the rules. You have to go all the way back to the start and try again.
The referee is the person who watches the whole line to make sure nobody sneaks ahead too early. They look very carefully to see if you were being naughty while the ball was in the air. If they see you being a bit sneaky, they stop the game and give the ball to the other team. It is not very fun to be caught, so it is much better to just wait your turn like a very good boy or girl.
Where the analogy breaks downIn a lunch queue, you can still stand in line even if you are not touching the food, but in football, being offside is about where you are standing the moment the ball is kicked.