"purposely" fumbling forward.

[ump76]

I had a situation that happened to a crew in our association and am confused on the enforcement and would like some help ffrom the gallery.

Team A is trailing by 5 points with :02 to go in the fourth quarter. They have the ball on B's 20 yard line and throw a pass to A1 as time expires. He cathches the ball on the 6 yard line and as he is being tackled, around the 5 yard line, he "fumbles" the ball into the end zone. His teammate A2 falls on the ball in the end zone.

Please explain to me B's options and what you would call in this situation. I appreciate your help.