Three moves in a row, each dissolving anger differently. (1) Suspension of judgement: τί δαὶ οἶδα εἰ τοῦτο ἁμάρτημα; — "and how do I know this was a fault?" The particle δαί is colloquial, near to "well now": the tone is domestic rather than philosophical, a man catching his own hand. (2) A concession with a rider: even if it was a fault, the offender has already passed sentence on himself. (3) An argument from nature: to wish a bad man not to go wrong is to wish the fig to be without juice.
What "clawing one's own face" means. καταδρύπτειν τὴν ἑαυτοῦ ὄψιν is a gesture of mourning: cheeks were torn with the nails over the dead. Marcus is saying that the offender has already mourned himself; the punishment has taken place, and to add one's anger to it is to strike a man already down. Cf. 11.18, where the same argument stands as one head of the protocol against anger.
A ladder of examples. συκῆ — βρέφη — ἵππος: a plant, an infant, an animal. Three levels of nature, and to demand something else of any of them is equally absurd. The fig tree is Marcus's standing example of the necessary (4.6, 8.15); here it comes first, and the series closes on the general ὅσα ἄλλα ἀναγκαῖα.
The turn in the last line. τί γὰρ πάθῃ τὴν ἕξιν ἔχων τοιαύτην; — "what is he to do, having such a state?" Ἕξις is a settled disposition, not a deed: to arraign a man for his ἕξις is as pointless as arraigning a horse for neighing. And the conclusion: εἰ οὖν γοργὸς εἶ, ταύτην θεράπευσον — "if you are brisk, cure it," that is, the ἕξις. Anger is not forbidden; its object is changed — from the man to his disposition, from accusation to treatment. The governing discipline is assent, the sustaining one action.