While that's the letter of the rule, in practice, what officials try to (or should do), is to make sure there are 6 on each side prior to handing the ball to the kicker, and then heading to the sideline, at which point the R whistles it in. So if, for example, there's 5 on the kicking team, I'll hold the ball until the 6th player gets out there, yelling to their sideline that they only have 5. The official on R's restraining line (H), should be alerting his sideline if they are receiving and only have 5, or alerting the other officials via radio or even just yelling across the the field, that they are short handed. As an H, I will usually come onto the field a bit so the the R can see there's an issue, and when the other player comes onto the field, is when I start retreating back to the sideline. That gives him a few seconds to get in place. We will do everything we can to get both teams ready. That said, we won't wait forever, especially if a team is repeatedly late getting their players out.
