Momentum has intrigued coaches and players, sport participants and researchers for years due to its ephemeral nature, association with success, and complexity as a subject of investigation. It is one of the most desirable, yet least understood performance experiences in social sport psychology. This study explored the experiential phenomenon of momentum, defined as an emotionally infused appraisal of current performance, using qualitative procedures involving 11 basketball players and coaches as informants. A case study helped highlight important features of what happens during instances of momentum. It was found that momentum is a hard to create but a valuable phenomenon for athletes and coaches, alike. Additionally, momentum seemed to elicit significant emotional, behavioral, and cognitive effects which constituted patterns of response to events in competition. These effects, manifested differently for players and coaches, occurred as performance appraisals and likely had considerable performance consequences for those experiencing it. This article will conclude with suggestions for practical application for both coaches and players and even fans who thrive on the ebb and flow of competitively spirited contests.