A View from the Bridge
Rodolpho is probably one the nicest antagonists in the history of drama. He's kind, respectful, artistic, and fun loving. Of course, our protagonist, Eddie, doesn't see it that way. To Eddie, Rodolpho is the lying, conniving, effeminate, "submarine" who's trying to steal away his beloved niece. Everything Eddie does in the first three-quarters of the play is to undermine Rodolpho. That makes the unfortunate immigrant our first antagonist.
For the last bit of the play, the antagonist torch is passed from Rodolpho to Marco. This is ironic, since Eddie liked Marco up until then. When Eddie betrays both brothers to Immigration, he makes an enemy of Marco. When Marco calls Eddie out on his betrayal in front of the whole neighborhood, he makes an enemy of Eddie. There you go: protagonist/antagonist. Note: when two characters duke it out at the end of a play, the chances are pretty good you've got a protagonist/antagonist relationship going on.