The term "must-win game" is vastly overused in baseball. Games are not must win until elimination hangs in the balance. There are games that probably should be won, need to be won for the sake of good feelings, and games that feel very important, but "must-win" is an exaggeration because the season will go on even if they aren't won. New York's three-game series against the Blue Jays in Toronto is not a must-win series because the Yankees are nearly guaranteed a spot in the playoffs. It is all but certainty at this point. However, there is certainly a must-win feel to the series because it feels like the team's last chance to really make a run at the AL East instead of the Wild Card.
Yankees vs. Blue Jays series preview: For all the marbles
