This is the beginning of a new part of the story where Matthew tells of growing opposition to Jesus's ministry. Here, the Pharisees criticize his disciples for picking grain on the Sabbath.
This is a place to plant grain. If wheat is unknown and "grain" is too general, then you can use "fields of the plant they made bread from." (See: [[rc://en/ta/man/jit/translate-unknown]])
Picking grain in others' fields and eating it was not considered stealing. The question was whether one could do this otherwise lawful activity on the Sabbath.