The Master

Freddie Quell is a sex-obsessed alcoholic World War II veteran from Lynn, Massachusetts, struggling to adjust to post-war society. By 1950, he has become a portrait photographer at a department store, but he is soon fired for getting into a drunken fight with a customer. Freddie then finds work at a Salinas, California cabbage farm, but his moonshine poisons one of the elderly Filipino migrant workers and he is chased off.
One night, intoxicated, Freddie finds himself in San Francisco and stows away on the yacht of a follower of Lancaster Dodd, the leader of a nascent philosophical movement known as "The Cause." When he is discovered, Dodd describes Freddie as "aberrated" and invites him to stay and attend the marriage of his daughter, Elizabeth, as long as he will make more of his mysterious brew (made with paint thinner), which Dodd has developed a taste for. Dodd begins an exercise with Freddie called Processing, a flurry of disturbing psychological questions aimed at conquering Freddie's past traumas. Freddie reveals that his father is dead, his mother is institutionalized, he had an incestuous relationship with his aunt, and he abandoned the love of his life, a young girl named Doris, who wrote to him while he was at war. Freddie is enthralled by Dodd, who doesn't flinch from his abject revelations, and Dodd sees something in Freddie. Freddie travels with Dodd's family as they spread the teachings of "The Cause" along the East Coast. Dodd and his family, with Freddie tagging along, stay as guests in the homes of various women drawn to "The Cause." But when at a dinner party in New York, a man questions Dodd's methods and statements, Freddie pursues him to his apartment and assaults him that night.
Other members of "The Cause" begin to worry about Freddie's behavior, despite Dodd's attachment to him. While they are guests of an acolyte in Philadelphia, Dodd's wife Peggy tells Freddie that he must quit drinking if he wishes to stay, to which he agrees. However, he has no true intention of keeping his promise. Freddie criticizes Dodd's son Val for disregarding his father's teachings, but Val tells Freddie that Dodd is making things up as he goes along. Dodd is arrested for practicing medicine without proper qualifications, after one of his former hostesses has a change of heart; Freddie is also arrested for assaulting the police officers. In the jail cell adjacent to Dodd, Freddie smashes the toilet and batters himself against the bars and his bunk, while Dodd tries to calm him. Freddie erupts in a tirade, questioning everything that Dodd has taught him and accuses him of being a fake. The two men trade insults until Dodd turns his back. They reconcile upon their release, but members of "The Cause" have become more suspicious and fearful of Freddie, believing him to be deranged or an undercover agent.
Freddie submits to additional exercises with "The Cause" but becomes increasingly angry and frustrated with the repetition of the exercises and his lack of results. Eventually he passes the tests, and they travel to Phoenix, Arizona, for the release of Dodd's latest book. But when Dodd's publisher criticizes the quality of the book and its teachings, Freddie assaults him. Helen Sullivan, their Philadelphia hostess, confronts Dodd in the lecture hall for suggesting that members should now "imagine" rather than "recall" the experiences of "other lives" in his new book, and he also loses his temper. During another exercise, in which Freddie is supposed to ride a motorcycle at high speed through the desert towards an object in the distance and then return, he instead abandons the group, riding the motorcycle out of the desert, and leaving Dodd and "The Cause" behind. He goes home to rekindle his relationship with Doris but learns from her mother that she has married and started a family in Alabama in the seven years since he last saw her. Freddie leaves disappointed.
While sleeping in a movie theater, Freddie receives a phone call (or dreams that he has) from Dodd, who is now residing in England. Freddie is asked to come join him. When Freddie arrives, he discovers Val is still in his father's employ and that Elizabeth has been expelled from the movement. Dodd seems happy to see him but Peggy tells him that Freddie has no intention of improving his life and that he should no longer be involved in "The Cause." Dodd changes his countenance, thinking his wife is correct. He gives Freddie an ultimatum: stay with "The Cause" and devote himself to it for the rest of his life or leave and never return. Freddie doesn't answer, expressing with silence his refusal. Dodd then comments that if Freddie can find a way to live without a master, any master, to let Dodd know because he'll be the first person in the history of the world to do so. Then Dodd serenades Freddie with the song Slow Boat to China. Freddie leaves and picks up a woman at a local pub, then repeats questions from his first processing session with Dodd as he is having sex with her. Finally, he appears to curl up on a beach next to the crude sand sculpture of a woman the sailors built during the war.

Question: Why was Dodd arrested?
Answer: Practicing medicine without proper qualifications.