From today's Under the Knife column by Will Carroll at Baseball Prospectus:
"Watching the Reds-Padres game yesterday, I wasn't surprised when David Ross got plowed by Mike Cameron on a close play at the plate. It was not--as the Reds announcer implied--a dirty play. Cameron didn't explode into him; he just dropped a shoulder rather than sliding, an accepted but dangerous play. Ross got the worst of it when Cameron's shoulder caught him on the chin of his goalie mask. It was driven back into his jaw and popped up and off his head. As Ross dropped, it was clear on the replays that his eyes closed, but it was also clear on the original play that Ross did what many trainers call "locking out." The arms seize and go rigid, often directly in front of the body at chest level. When that occurs, the player has lost consciousness and by definition is now in Grade II on the concussion scale. So after several minutes passed with Ross on the ground, then slowly sitting up, and finally coming to his feet and making a couple wobbly steps, how did the trainers decide to let him stay in the game? Ross made it through the inning, but the risk he took--being in a situation where the ball was coming at him at 90mph and the concussion could easily have been exacerbated--makes me wonder what the trainers saw there."