They Reinterpreted the Law

Matthew 16:12, “Then they understood that he did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees.”

“Pharisees. As the party of the synagogue, the Pharisees strove to reinterpret the law.” NIV Study Bible Notes

In example, when the Pharisees said the disciples did not wash their hands they were referring to ceremonial washing, (Mark 7:1-8). That is, making a fist and washing your hands up to the elbow. (If their hands were dirty, they stayed dirty!)

The disciples had clean hands, but could not perform the ceremonial washing because it was to be done when you entered a house. They were walking through the fields. (That is why there were large pots of water at the wedding at Cana.)