The Kuzy hit was a legitimate check that just happened to catch him the wrong way. It happens, and it's unfortunate that the outcome of the series could be decided by a piece of bad luck like this, but it is what it is.
Two weeks before the 1975 playoffs the Boston Red Sox lost one of their premiere players when Jim Rice was hit in the arm by a pitch and broke it. The Sox got to the World Series that year and lost to the Cincinnati Reds in the 9th inning of game 7. To this day Sox fans imagine how different it might have been if Rice had been available for the World Series, but he wasn't, and the franchise had to wait almost another 30 years to get its elusive championship -- by which time all the players on the 1975 team were long gone, of course. That is the way things happen.