How many letters does the top answer for “the failure to obey” have?

The most common answer is disobedience (12 letters).

Crossword clue: the failure to obey

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

disobedience 12 letters wn-def

the failure to obey

noncompliance 13 letters wn-def

the failure to obey

neglect of obedience; failure to obey. 50% similar → nonobedience