"Harmless" is one of the last words I'd use to describe Madsen. He's nearly the opposite; "pesky" is a good adjective for him. I like his game, actually, but I'm not at all surprised if he occasionally irritates opposing players. Dice obviously was sick of him, and gave him an unneccesary shove. It's hard to say if it was warranted, because we have no idea what kinds of things were happening in the minutes leading up to the shove. Maybe Madsen caught him with an elbow or something.
Watching the replay, I don't think KG really expected Antonio to be so confrontational. KG gave Dice a very weak little shove, and probably expected that to be the end of it. Instead, Antonio shoved him back harder. KG's not going to take that, so he threw the ball, and then things escalated a little.
Overall, a very minor incident. Nothing like the New York/Denver fracas.