What Duncan did yesterday was dirty, no other explanation can change it! What Johnson did, while not a dirty play, was probably a bit to aggressive for a spring training game, especially between two minor league players. As for Girardi, I haven't seen a story yet today that mentions his approval or disapproval of what Duncan did yesterday.
What I do see here though is folks who would condone a pitcher throwing a 90 + MPH fastball at a batter in retaliation but who disapprove of a position player sliding cleat high. Personally, I don't see a difference. Both actions can result in serious injury and both are dirty. So, the next time people post here that they hope A-Rod or Jeter or anyone else gets drilled, remember how you weighed in on this issue with Duncan.