The play is most similar to this. I would call a delay of game warning on Team B.
*7.5.1 SITUATION B:
Team A does not break the huddle after the second horn
for a 60-second time-out. The official puts the ball down at the designated spot
and begins the five-second count. The administering official is between four and
five on the count when Team B reaches over the boundary and grabs the ball.
RULING:
Delay-of-game warning on Team B for reaching across the plane. No
Team A member ever possessed the ball for the throw-in; therefore, a technical
foul would not be assessed. (9-2 Penalty 3)