Lotsa' luck to the court collecting on that!
Typically it is a misdemeanor to be on posted property. It rises to a felony if you stay there after being told to leave (defiant trespass), or if there is another crime involved, such as breaking into an outbuilding.
The problem here is detaining someone after simple trespass - he can confront them and ask them to leave, and if they oblige and start walking for the property border, that means the trespass remains at the misdemeanor level.
This is why the Minutemen were smart to just observe, not detain.