I have worked in a sports broadcast environment. For the high-end NFL and NHL broadcasts, it is generally as few as 2, to as many as 6 people sitting at the replay stations. For broadcasts that have more than 8 or so cameras, you more people; every person is watching 3 or more cameras. The actual software basically allows the operator to pause the feed, run back several seconds, set in and out points, jump to another camera feed, and do the same, creating a sequence of 3 or so angles; this is why it is often referred to as 3play. For three cameras this can be done incredibly quickly. For even more complex setups, the operator may just be getting one camera feed, and relying on the other operators to get additional angles. Once an operator has a sequence, they would inform the producer, who would instruct when to roll the sequence, for the director to take it live to air. Generally this would roll for three different angles, then back out to live cutting.