Why does everyone run back to their starting positions after a goal has been scored?
All team mates are responsible for getting themselves on-side between a goal being scored and the Centre pass. If you are not on-side (behind the transverse lines) before the Centre steps into the Centre circle, you are DELAYING PLAY. Centre must not wait for players to get on-side before stepping into the Centre circle, otherwise Centre is delaying play. Therefore, run straight back to your starting position as soon as a goal is scored.
Delaying Play does not exclusively happen on a Centre Pass. For example, a player taking too long to position themselves for a penalty, or (un)helpfully throwing the ball away from the opposition who has awarded a sanction could also be deemed as delaying play.
NOTE: Delaying Play is now the only sanction that is advanced.