The fields didn't fully allow knife fights. High speed impacts the shield would repel but slow but strong movements with a knife could penetrate it. The way the

The fields didn't fully allow knife fights. High speed impacts the shield would repel but slow but strong movements with a knife could penetrate it. The way the movie at least justified disabling the shields was that the Fremen were seen to use laser weapons which in the Dune universe would cause a mini nuclear explosion if they hit a shield.