It is a good question. I asked the same question here about 5-6 years ago.

You could refer to these:
2011-12 NFHS Basketball Rules Interpretations

SITUATION 3: A1 has the ball for an end-line throw-in in his/her backcourt. The administering official reaches a four-second count when A1 passes the ball onto the court. A1’s pass to A2, who is also in Team A’s backcourt, takes several bounces and six seconds before A2 picks up and controls the ball. RULING: Legal. Even though a team is now in control during a throw-in, the 10-second rule specifically requires that a player/team be in continuous control in its backcourt for 10 seconds for a violation to occur. Technically speaking, the thrower-in is out of bounds and not located in the backcourt. (4-35-2; 9-8)

SITUATION 5: A1 has the ball for an end-line throw-in in his/her frontcourt. A1’s pass to A2, who is in the frontcourt standing near the division line, is high and deflects off A2’s hand and goes into Team A’s backcourt. A2 is then the first to control the ball in Team A’s backcourt. RULING: Legal. There is no backcourt violation since player and team control had not yet been established in Team A’s frontcourt before the ball went into Team A’s backcourt. The throw-in ends when A2 legally touches the ball, but the backcourt count does not start until A2 gains control in his/her backcourt. (4-12-2d; 9-9)

These interpretations actually do not address the question at hand. In situation 3, the interpretation says there is no 10 second count because 4 of those seconds were during the throw-in which doesn't count towards the 10. That's already covered in the rule book. It doesn't actually state whether the ten second count should start when the player gains control or when the ball strikes the floor in the backcourt.

The second interpretation applies to backcourt violations, and it does change the rule "as stated" in the book (the book says for backcourt that only team control is necessary in the front court, this interpretation says otherwise). However it doesn't do anything to help us when deciding to begin counting ten seconds.

Read number 5 again -- especially the last sentence:

The throw-in ends when A2 legally touches the ball, but the backcourt count does not start until A2 gains control in his/her backcourt.

Situation 4 makes the same point.

Got it. Thanks.

Is this point only available through prior years interpretations?

It's one of the complications with the way they added to the team control definition.

My opinion is that it would be nice if a more clearly defined criteria for when a 10-second count starts was put in words in the rule book.

When the rule was written, there was no team control during a throw-in at the HS level, so the "continuously in team control" phrase made sense. Now it's convoluted with the addition of TC fouls on throw-ins.

They've tried to do this by interpretation. The problem is, interps fade over time. I'm already talking to veteran officials, association leadership, who are insisting that, by rule, the throwin that is tipped by A in the FC and recovered by A in the BC is a violation.

westneat is correct in that the rule itself has this as a violation: but the NFHS was clear when they added TC to the throw in that they did not want it to apply to anything except whether you shoot FTs on a given foul.

The need to change the TC rule back, and then simply change the penalties to state that a foul committed by the throw in team does not result in FTs. Maybe include that in the definition of a TC foul, even though there's no TC. This wouldn't be any different than a PC foul that can be charged even when there's no PC. I believe this was Bob's suggestion.

Agree 100%. In fact, I've lobbied the current and previous Rules Committee members from my region to do exactly that. It's gotten nowhere. (What makes it worse is that the current committee member is an official.)

They've already (kind of, almost) done this. They included the inbounder in the definition of team control foul (4-19-7). The rule could be made a little clearer, and then just eliminate team control during the throw-in. I wish they would do this and eliminate all this confusion and contradiction.

Worse, unless it's in the book, how can I justify a call that looks like it directly contradicts the rulebook?

You won't have to -- at least for a while.

This is one of the (rare) times when "what everyone knows" is correct.

Note that the NCAA rule is a little different -- the shot-clock starts when the ball is touched and when it gets to 20/25, it's a violation -- even if there was never PC in the BC. (generic statement only, for the usual situation; I recognize there are exceptions.) So, once people get used to that, then you might have some explaining to do, if FED doesn't clarify.

Unfortunately, the great majority of HS officials that I see, start the 10 second count upon the first touching of the ball, rather than control.

Who would've thought I'd see it so soon...
 

Did some men's "wreck" last night to try and make up a few dollars since my last FIVE HS games were cancelled. Had a play where white got a rebound and then lost the ball in transition still in the backcourt. A player from Red dove on the ground and had one hand firmly pinning the the ball to the ground near the mid-court line, but clearly in Red's frontcourt. He then put his other hand on the ground to push himself up, but put it down in the backcourt. I blew for a backcourt violation and then thought about this thread instantly and wondered if maybe I jumped the gun because it seemed to me the consensus here was that one hand pinning the ball to the ground is not control.

I don't recall seeing anything "official" about whether pinning the ball to the ground was control. I suppose it depends on how you define "holding".

As the poster formerly known as Snaqwells would say, would you grant a time-out in this situation?