Barnes may have been upset with a screen from Stiemsma and reacted by pushing the center. He was ejected immediately after being assessed with a flagrant 2 foul.
Stiemsma must have still been upset over the uncalled for shove from Barnes, because he retaliated a minute later.
Stiemsma pushed Grant Hill to the ground while Hill was attempting to rebound an Alexey Shved miss. Stiemsma dangerously timed his push, waiting until Hill was in the air and unable to protect himself. He was assessed a flagrant 1 foul for the act.