"purposely" fumbling forward.

[Texoma_LJ]

Assuming that the penalty is an illegal forward pass, the options should be as such:
If Team B declines, then it is a touchdown for Team A
If Team B accepts the penalty, then it would be 5 yards marked off at the spot of the foul. Since the period cannot end on a any ppenalty that is accepted, Team A is then given one untimed down.