Safety is everyones concern, whether you are a competitor, official, or a spectator.  The rules in motocross aim to provide a safe environment for riders to enjoy their sport.  MNZ have a comprehensive document that outlines the rules, the Manual of Motorcycle Sport

Flags

Races have flags that signal riders about certain conditions, or stages of the race.

Yellow   Held stationary or Waved – SLOW DOWN NOW – Proceed with extreme caution, No overtaking until the danger is passed, be prepared to stop. Whether the yellow flag be stationary or waved this means no jumping at all. A jump is defined when any wheels are not continuously in contact with the ground. Riders are not to use the yellow flag to gain an advantage on a fellow rider. Any competitor that is seen to gain an advantage may be penalised. 

White   Last lap. 

Black & White Check   Finish for all riders.

Red   All riders stop racing.

Black   Individual rider to stop and retire from course. The rider’s number must be shown on a board at the same point as the black flag is displayed.

White Flag with Red Cross   Ambulance or Medical personnel on course proceed with caution. 

Purple Flag   protest flag

Rules

Here are some basic rules, definitions and advice from the MNZ website.

Riding Backwards   You may never ride or push your motorcycle in the opposite direction to the race/track.

Outside Assistance   A competitor may not receive any outside assistance during the race. Mini or Junior Motocross riders can have their bikes lifted and restarted but no pushing is permitted to assist the rider.

If your machine stops   A competitor whose machine has stopped on the course should not jeopardise the chances or safety of others by staying on course to make adjustments repairs or restart their machine. They must move as far away from the track as is safely possible.

Stopping a race   If, in the opinion of the Steward or the Clerk of the Course it would be dangerous for a race to continue, the race may be stopped.

Leaving or cutting the course   The Steward or Clerk of Course of a meeting can exclude any competitor who has gained an advantage by leaving the track, unless such action was for the safety of other competitors or was due to the action of another competitor.

Foul or Dangerous Riding   The Steward or Clerk of Course of the meeting will exclude any competitor who in their opinion is guilty of any foul, unfair or dangerous conduct. The Steward may also declare the race void if, in their opinion, an offending rider jeopardised the fair chances of one or more of the other riders.

Punctuality in Starting   Any competitor not ready to start on time may be considered a non starter.

Practice for a competition   Only competitors entering an event shall participate in any practice for the particular competition for which they have entered.

Start and Finish Line   The crossing of the starting and finishing line in speed events is when any part of the machine passes over the line. The actual time of the start and finish of the race shall be taken when the order to start is given or when the staring line is crossed, according to the method of start, and when the finishing line is crossed.

Drugs and Alcohol   Drugs, alcohol and sport do not mix. MNZ has adopted the Drug Free Sport’s Anti-Doping policy.

Impounding a Motorcycle   The Stewards of a meeting may order any motorcycle, which they have reason to believe may not be in accordance with the MoMS or Supp Regs, to be impounded at the end of the meeting. The motorcycle may be retained until it is examined.

Bike Numbers   There are specific requirements concerning racing numbers, number plates, types of numbers etc. These are strictly enforced for Championship level riders. Before you select a number or make a number plate for your bike, check with MNZ as to the allocation of numbers and number plate requirements. Rules relating to number plates are contained in Chapter 10 of the MoMS.

Injuries   If you suffer an injury at an event that requires further medical attention (i.e. you are referred to Hospital), the Steward will keep your MNZ Licence and send it to the MNZ Office. You will be placed on the “Restricted Riders” list and will not be able to compete until a medical clearance is sent to the office stating that you are fit to compete in motorcycle racing. You are automatically stood down from racing for 21 days if you suffer from a concussion or suspected concussion.