Field help (NCSREASON) 

Use this field to summarize the reason why this problem arose in the first place. You should use this field to support the identified root cause following root cause analysis. This field is mandatory.

 If your selected reason could potentially lead to further questions being asked about the root cause then you are advised to further analyze the root cause.

The list of reasons for raising a non-conformance is defined in Miscellaneous table 802 - Reasons for Non-conformance.