{They that were of the circumcision} (hoi ek peritom(8873)).
Literally, those of circumcision (on the side of circumcision, of
the circumcision party). The phrase in  10:46  is confined to the
six brethren with Peter in Caesarea ( 11:12 ). That can hardly be
the meaning here for it would mean that they were the ones who
brought the charge against Peter though Hort takes this view. All
the disciples in Jerusalem were Jews so that it can hardly mean
the whole body. In  Ga 2:12  the phrase has the narrower sense of
the Judaizing or Pharisaic wing of the disciples ( Ac 15:5 ) who
made circumcision necessary for all Gentile converts. Probably
here by anticipation Luke so describes the beginning of that
great controversy. The objectors probably did not know of Peter's
vision at Joppa, but only of the revolutionary conduct of Peter
in Caesarea. These extremists who spoke probably had abundant
sympathy in their protest. The apostles are mentioned in verse
 1 , but are not referred to in verse  2 . Apparently they are in
contrast with the circumcision party in the church. {Contended}
(diekrinonto). Imperfect middle of the common verb diakrin(935c),
to {separate}. Here to separate oneself apart (dia), to take
sides against, to make a cleavage (dia, two, in two) as in
 Jude 1:9 . So Peter is at once put on the defensive as the
contention went on. It is plain that Peter was not regarded as
any kind of pope or overlord.