Loving this debate in regards to sportsmanship.
First of all, NZ didn't do anything wrong. Was within the laws of the game, and Murali knew better. And to be quite honest, I don't think McCullum saw Murali initially going to congratulate his partner on 100. We're all seeing this with the benefit of hindsight and television replays. Remember, it's a fast game and McCullum would've been watching the ball coming in. He gets the ball, sees and turns the batsman is out of his crease and whips off the bails.
In fact, if you watch the video replay of the run out, in two angles you can plainly see Brendon McCullum watching the ball with his back to Murali as Murali touches his bat down and sets off to congratulate. McCullum collects the ball, turns and takes out the stumps.
There's been two signs of complacent cricket here - one from Murali and one from the umpire, getting too far ahead of themselves in the state of play.
Sportsmanship. In cricket, as far as I'm concerned, sportsmanship applies mainly off the field and in between the action.
For example - it's sportsmanship to congratulate a batsman on their hundred, or fifty, or to clap the opposition captain on/off a field, etc.
However, in between the time that the ball is bowled and the ball is dead, all sportsmanship goes out the window. As mentioned earlier (I think, in another thread) if a batsman falls while taking a run and he's out of the crease, you don't go and help him up while the ball is live and play is happening. Quite simply, you run him out. THEN you go and help him up.
The football analogy with the goalie was used before. Another one might be in league or union. If the ball is kicked and a guy on the opposite team drops the catch, fumbling it to one of your guys giving you an opportunity to score a try, you'll score a try. You won't say "oh hard luck on dropping the catch. Here, have another go?"
No. Because that's not professional. At this level, what McCullum did was professional and in the best interests of his team. I don't think he did anything wrong professional-wise or sportsman-wise.
If you want to get on the subject of sportsmanship in regards to Sri Lanka, what about Prasanna Jayawardene holding onto the ball for longer than normal, hoping the batsman would leave his crease to do gardening, or something similar?
If the excuse is "because NZ did it" then automatically, NZ did nothing wrong.
If the excuse is "to get a wicket" then thats fine, because thats what NZ did.