1 chance in 1, as per the photographic evidence above. The odds of a past event happening is always 1:1 because it happened. (I know, I know, people hate being told that.)

So I recognize that the spirit of this question is really about "objective" probability.

Unfortunately, I can't find data on how much time a basketball player spends in a game without making contact with the floor. Not surprising. It could be found if you wanted to go through video of games, I think. That would also be the most useful way of determining when six people (five players and one referee in this picture) are clear of the floor.

Especially because being all of similar height and athletic ability and moving at the same speed, they'll have similar strides, and one's options in basketball are highly dependent on foot placement. Syncing up strides (as the photo also demonstrates) even subconsciously wouldn't be surprising.

So, with those factors off the top of my head, I don't think this is a calculable answer outside of simply collecting a large data set of basketball photos and extracting statistics.