Throw In - Ball at disposal of a player

[PG_Ref]

Originally Posted by Adam

You would be wrong. The rule is the team has 5 seconds to release the throw in pass, how could you start the 5 second count before he is able to release that throw in pass?
In your OP, you grant the TO until B is legally able to execute a throw-in pass. "At the disposal" is meant to give the official leeway if B is taking more than a reasonable amount of time to get OOB and release a throw in.

See the below caseplay

4.42.3 SITUATION:

Following a goal by A1 the ball is: (a) inadvertently deflected under the bleachers; (b) bouncing on the court just outside the end line as B1 makes his/her way toward the ball; or (c) lying on the court just outside the end line as B1 delays the inbound by getting instruction from his/her coach. When does the throw-in begin and the ball become live?

RULING: In (a), the official shall signal for the clock to be stopped. The throw-in begins and the ball becomes live when it is at the disposal of Team B. In (b) and (c), the throw-in begins and the ball becomes live when it is available to B1 and the official begins the throw-in count. In (c), the throw-in count begins when the official determines B1 has had ample time to secure the ball; it need not be in B1's possession. (4-4-7d)