Don't panic, ever. Don't do the police's job, ever. If police are the cause of the injury, the second marshal should directly contact an ambulance service. When the march has gone by, don't dissolve until there is another red light to protect marshalls. When you're rushing to get to the next intersection, try to make it seem as if you're not panicking or creating a riot.
Marshals are the primary communication link between police and demonstrators.
Marshals should approach police confidently but not aggressively. It is also best to approach police with caution, but not with suspicion. Nevertheless, it is possible that police may act aggressively. Try to be calm during a confrontation with a cop. Any physical contact with a police officer on duty can result in a criminal charge of assault.