The point, late in a game, when teams/players have to step up and play their best in order to secure a victory. The game score must be close near the end in order for "crunch time" to be the appropriate term. This term can be used in reference to various sports, but is primarily a basketball term.
According to the Merriam-Webster dictionary, the term "crunch time" has been in use since 1976. It is incredibly important for teams and players to perform well in crunch time, as those are the moments that separate the good from the great. Teams and players alike have built long-standing reputations based on crunch time performance (positive or negative).
Basketball analyst Clark Kellogg has said, "It's not what you do, but when you do it," referring to the fact that players who come up big late in close games are more valuable that those who put up good numbers, but don't get it done when it counts most. If you have the heart of a champion, crunch time is something you relish.