Australian vice-captain David Warner called Quinton de Kock a "f***ing sook" in the moment immediately before their incident in the tunnel during tea in the first Test match in Durban.
"Dave is at his best as a cricketer when he is in the face of oppositions, he is very good at getting under their skin and it's been clear in the first Test that he has been able to do that", Paine said.
Paine added that had Warner been able to get any closer to De Kock, there was no telling what he would have done.
"When you are bringing people's families or wives into it it's unacceptable".
The Proteas are understood to be disappointed that Warner didn't receive a level-three charge from the ICC, something that would have ruled him out of the second Test in Port Elizabeth.
Meanwhile, de Kock has reportedly contested his level 1 charge against him and will attend a hearing in Port Elizabeth on Wednesday evening.
Du Plessis said on Monday: "All I've heard is there was a lot of personal stuff on the field already, to and from (both sides)".
"Respect is the key & and I hope nothing personal was said to any player towards anyone from either side".
"We're certainly supporting David".
"There was nothing we said that was inappropriate".