Why would it happen against Porter? It's not like Kell was gonna turn up unprepared and under-trained for his first title fight. Plus Porter isn't tall enough to accidentally head butt Brook in the nose like Jones did. Kell past a gut check. A lot of guys fall like lawn chairs. Kell didn't. Then he wiped his bum with Jones in a rematch. :nod
He appeared to be stopped by an injury caused by the punch rather than the fact he was too hurt and/or dazed to continue.