IAW 4-25, "both opponents" need to have their hands on the ball for you to put air in your whistle for a held ball.
A1 ends his dribble. B1 reaches in an tips the ball away. A1 momentarily fumbles the ball in the air, and it becomes wedged between A1's forearm and body. B1 reaches in and grabs the ball with both hands, but is unable to take it awayl A1 and B1 begin wrestling for control of the ball which remains wedged between A1's body and forearm and B1 has both hands on the ball.
Seems not to meet the definition. Do you blow it dead or let them wrestle until something eventually happens - foul, loose ball, etc?