In this paper, I tryed to understand how the new possibilities of a growing media (the French television in the Seventies) change the “live broadcast” of a major sport event — concerning a sport, cycling, whose audio-visual treatment is definitely delicate. After observing how the press mixes several representation modalities (graphic, photographic, textual), I analysed the way the audio-visual stream builts during a deciding stage of the 1975’s Tour de France. Two phenomenons kept my attention : on the one hand, the extreme enunciative complexity of the live commentary — which reveals a new type or even a new genre on a modernized medium ; on the other hand, the rise in uncertainty. Although we could expect that television, as it pretends, would build a perfect broadcast, the new narration ways lead us to a surprising result : the dramatized building of a narrative that is still faulty.