People who enforce the law can include:

• Police officers -- the most obivous group.
• Code enforcement officials -- these are people in US cities who check to make sure people are following laws about things like not letting trash pile up in your yard.
• Tax auditors -- check to make sure you aren't cheating on taxes.
• School officials -- enforce laws having to do with education.

Trial by ordeal was based on the idea that God would ensure a just decision in a trial.  So you could have one person accuse another of something and the two would be ordered to fight.  Whoever won must have God on his side and so he must be telling the truth.