Because the baton in his hand had gone missing without him even seeing how it had happened. The chief security guard was about to tell the other security guards to watch out when the baton hit him in the back.
It knocked the wind out of him, and he crashed onto the floor. He never wanted to experience this again, so he played dead. Since Darius was so powerful, there was no point in him putting up a fight because he wouldn't stand a chance against him. If everyone here were going to receive a