I heard on the radio that Biden interrupted Trump about 60-something times, whereas Trump interrupted Biden about 140-ish times? Also noted, the first to interrupt someone was Biden, who did it three times before Trump got to interrupt Biden.
I just rewatched the first part of the debate, and I assume they are talking about quick responses biden gave as trump was speaking during the open discussion part of the debate after the first question.
Bidens allowed to give responses in that part of the debate, it's open discussion, Though one can argue if it even properly should be open discussion at that point. The moderator never got to actually declare open discussion, Trump just starts talking the moment bidens 2 minutes expired after the first question, pretty much starting open discussion on his own.
The first instance of someone outright saying whole sentences over someone else trying to speak is trump during that open discussion.
But lets say that's all fair enough.
Personally I would say the first section of the debate is.. mostly acceptable from both sides, neither going egregiously over the line.
Following that first segment, trump starts arguing with wallace when he tries to ask his health care question. You could call that the first interruption, but again it's not during the 2 minute exclusive period.
The first solid example of someone talking over someones exclusive 2 minute period appears to be Trump talking over Biden in the health care question approximately 12 minutes into the debate.
Regardless of who started it though, there's no question watching the debate that Trump is the problem. He's the one literally arguing with the Wallace instead of Biden because he can't seem to tolerate letting the moderator ask the question without immediately retorting.
No doubt Biden did some interrupting too. But what exactly is he supposed to do? If he stays silent that'll just be playing into Trumps sleepy joe image.