In Romeo and Juliet by William Shakespeare, what things does the Friar do that are illegal or frowned upon?

The most important thing the Friar does is the central event of the play: he marries Romeo and Juliet. The two lovers are from feuding families, the Montagues and the Capulets, and thus their parents would never approve of their relationship. This is why the act of marrying the two is illegal. Lord Capulet would have to agree to allow his daughter to marry Romeo for the wedding to be legal. In fact, Lord Capulet is involved in negotiations with Paris to marry Juliet even as she marries Romeo behind his back. The Friar agrees to undertake this fateful marriage because he hopes, as he tells Romeo in Act II, to turn "your households' rancour to pure love." In other words, he hopes that he might end the feud between the Capulets and Montagues through the marriage. In a sense, this illegal act works, because the two families are reconciled when they find their children dead. The Friar also acts illegally when he gives Juliet the sleeping potion, and possibly when he sends a message to Romeo, who has been banished for the death of Tybalt. He confesses all of this after Romeo, Juliet, and Paris are found dead at the Capulet family crypt. The Friar acts illegally in the hopes that his actions might end the bloody feud that has gripped Verona.