The Dolphins were facing a 3rd and goal at the Lions' five-yard-line during the sequence. Quarterback Brock Osweiler stepped back and launched a pass to the back right corner of the end zone, finding Stills just before he ran out of bounds.
Stills made the catch, but was pushed by cornerback Darius Slay just as he turned his head forward.
He slammed ran directly into a nearby security guard and forced her to fall to the ground hard. The woman hit her head on the wall behind the end zone and appeared to be in significant pain before she was attended to.
Stills gave the woman the football while checking on her status.
The Dolphins trailed the Lions 17-7 at halftime.