Actually had this happen.
Ball carrier A11 is running off-tackle to the left when an opponent grabs his facemask (big time, foul called), and pulls the helmet off, which causes A11 to fumble. The ball bounces hard left about 5 yards, with A11 in chase. The ball manages to bounce off another player back toward A11, who recovers while going to the ground. From fumble to recovery was approx 2-full seconds.
Hmm. What to do now? Do we consider A11’s action continued participation? Or does this qualify as “…the immediate action of which they are engaged”?
We went with FMM only, and allowed A11 to remain in the game.
What would you have done?