From ESPN:
"It was uncalled for," Pierce said. "I reacted at the moment. That's all it was. We handled it like men. I apologized to the team this morning and we move on."
Pierce said that he and Rivers had not talked things out, but the conversation doesn't need to be a long one.
"He's the coach," Pierce said. "Whatever he says goes, and that's it."
He did the right thing and deserves credit for that. Nothing more to say really.