When does a slide begin?

[UmpJM]

Don M.,

While I cannot find anything definitive in the FED Rule or Casebook, this sounds to me like an illegal slide under FED rules.

My rationale is that the runner is "airborne" at the time he makes contact with the fielder who is in possession of the ball. On a "feet first" slide, the runner explicitly must no longer be airborne. I would apply the same principle in this sitch.

Of course, I could be wrong.

JM