Team spirit can go along way in winning a game. I have seen teams that didn't seem to have much in the way of brut talent come out on top, because the team supported each other. If you have one or two players hot dogging it on the field, trying to take all the glory for themselves; the team can't possibly be all they can be.
Team spirit and fan support are two of the most important factors, other than actual talent, when it comes to inspiring a team to put forth the extra effort needed in some games. If the fans give up on them, team spirit runs the risk of fading.