They noticed that some of his disciples weren't being careful with ritual washings before meals.
The Pharisees - Jews in general, in fact - would never eat a meal without going through the motions of a ritual hand-washing,
with an especially vigorous scrubbing if they had just come from the market (to say nothing of the scourings they'd give jugs and pots and pans).
Published by permission. Originally published by NavPress in English as THE MESSAGE: The Bible in Contemporary Language copyright 2002 by Eugene Peterson. All rights reserved. (The Message Bible Online)