[Lotto]

The NCAA rules (what we use for HS here in NY) has it explicity:

Rule 5-10, Art. 12: During a 30-second timeout, players shall stand inside the boundary line.

...and new this year:

Art. 13. During any timeout, bench personnel and players shall locate themselves inside an imaginary rectangle formed by the boundaries of the sideline (including the bench), end line, and an imaginary line
extended from the free-throw lane line nearest the bench area meeting an imaginary line extended from the coaching-box line.