Albert Barnes Commentary Ruth 2:9

"Let thine eyes be on the field that they do reap, and go thou after them: have I not charged the young men that they shall not touch thee? and when thou art athirst, go unto the vessels, and drink of that which the young men have drawn." — Ruth 2:9 (ASV)

After them - that is, “after my maidens.” The fields not being divided by hedges, but only by unplowed ridges, it would be easy for her to stray from Boaz’s land without being aware of it, and so find herself among strangers where Boaz could not protect her.