McEnroe was taunting Connors the whole match. At point he looked like he is going to wack the ball at Jimmy on the other side of the court. Connors was no angel either, btw.
There used to be a video clip on the web called "McEnroe storms off" taken from that match. If it ever shows up again, watch it. It shows what Connors was upset about.
Ahh, the good ole days.