This might be inferred from context as well as different translations for that crucial word.
καταγινώσκω (kataginōskō) 'to condemn' (G2607)
to condemn, convict; (pass.) to be in the wrong, condemned
Ionic dialect and later καταγηρ-γῑνώσκω, future -γνώσομαι[Refs 5th c.BC+]:—remark, observe, esp. something to one's prejudice, with genitive person:
__I generally, καταγνοὺς τοῦ γέροντος τοὺς τρόπους having observed his foibles, [Refs 5th c.BC+]; πολλήν γέ μου δυστυχίαν κατέγνωκας I have been very unfortunate by your way of it, [Refs 5th c.BC+]; οὐκ ἐπιτήδεα κατά τινος κ. having formed unfavourable prejudices against one, [Refs 5th c.BC+]: with infinitive, of an unfavourable judgement, κ. ἑαυτοῦ μὴ περιέσεσθαι [Refs 5th c.BC+] despising us because.. [Refs 5th c.BC+]: with participle, κ. τινὰ πράττοντα [Refs 5th c.BC+]:—passive, to be judged unfavourably, lightly esteemed, παρολιγωρεῖσθαι καὶ καταγινώσκεσθαι [Refs 2nd c.BC+]; κατεγνωσμένος despised, [Refs 2nd c.AD+]
__II with accusative criminis, lay as a charge against a person, κ. ἑωυτῶν ἀνανδρείην [Refs 5th c.BC+]; δειλίαν, δωροδοκίαν κ. τινός, [Refs 5th c.BC+]; πολλὴν μανίαν, μωρίαν, [Refs 5th c.BC+]passive, καταγνωσθεὶς δειλίαν being convicted of cowardice, [Refs 1st c.BC+]self-condemned, [NT]
__II.2 with genitive criminis, παρανόμων κ. τινός [Refs 4th c.BC+] pronounce a verdict of murder against.. , Legal cited in [Refs 5th c.BC+]; μὴ καταγιγνώσκωμεν τὸ (perhaps τοῦ) μηδὲν εἰρηκέναι τὸν ἀποφηνάμενον [Refs 5th c.BC+]
__II.3 with infinitive, κ. σφῶν αὐτῶν, ἑαυτοῦ ἀδικεῖν, charge oneself with.. , [Refs 5th c.BC+]passive, καταγνωσθεὶς νεώτερα πρήσσειν being suspected of doing, [Refs 5th c.BC+]; κ. αὐθέντης (i.e. εἶναι) [Refs 5th c.BC+]; to be detected, ἔν τινι [Refs 3rd c.AD+]; also κατέγνωσται μελίκρητον ὑπὸ τῶν ἀνθρώπων ὡς καταγυιοῖ τοὺς πίνοντας [Refs 5th c.BC+]
__II.4 with genitive person only, condemn, τοῦ ἀνθρώπου [Refs 5th c.BC+]
__III with accusative poenae, give judgement or sentence against a person, κ. τινὸς θάνατον pass sentence of death on one, [Refs 5th c.BC+]; Μηδισμοῦ κ. τινὸς θάνατον for Medism, [Refs 5th c.BC+]: with infinitive, κ. αὐτοῦ ἀποτεῖσαι τὰ Χρήματα [Refs 4th c.BC+]; later θάνατον, φυγὴν κ. κατά τινος, [Refs 1st c.BC+]:—passive, θάνατός τινος κατέγνωστο [Refs 5th c.BC+] they were condemned, [Refs 5th c.BC+]
__III.2 decide a suit, δίκην [Refs 5th c.BC+]:— passive, [Refs 5th c.BC+]
And this can be rendered as
NET: But when Cephas came to Antioch, I opposed him to his face, because he had clearly done wrong.
YLT: And when Peter came to Antioch, to the face I stood up against him, because he was blameworthy,
From the context (that later in the text is explained) we can see that Paul very heavily criticises Peter for doing the 'right' thing before – behaving like Paul and eating together with all gentile Christians – and going back on that when more traditionally oriented missionaries came with their Jerusalem, more Jewish/Judeo-Christian interpretation of the 'right' religion and the 'right' behaviour.
The funny thing here is that it might be read as a double entendre: Peter was sitting between two chairs and couldn't make it right for everyone. He was therefore condemned/blamed by the James-people for doing it like Paul and then also by Paul for doing what the James-people wanted of him.
Paul the outsider was accepted into theJewish-Christianity community; the second section (2: 1-10) shows how Paul's gospel and mission were officially recognized by the Jerusalem authorities against the opposition; the third section shows how the original agreements were broken, partly as the result of historical developments, partly by human failure, especially of Peter.
Paul contends that he has faithfully maintained the same position which he had always defended and which had been approved by theJerusalem authorities and indeed by God himself.
The facts are simple: for reasons not spelled out Cephas had come to Antioch and taken up table fellowship with the Gentile Christians, and perhaps even the Gentile way of life altogether. For whatever reason, this was considered proper by all people present.
Then, again for reasons unknown, a delegation of "men from James" arrived. Pressured by them, Cephas and the other Jewish Christians reversed themselves and withdrew from the fellowship with their Gentile fellow Christians. They took up again the Jewish way of life, especially the part of ritual separation from the unclean. Paul did not follow the other Jewish Christians' action, but stayed with the Gentiles and confronted Cephas in an open debate.
The result of this confrontation is unknown. It appears that the break between Paul and the other Jewish-Christian missionaries, including his former mentor Barnabas, was irreparable.
–– Hans Dieter Betz: "Galatians", Hermeneia –– A Critical and Historical Commentary on the Bible, Fortress Press: Philadelphia, 1979.