Arroyo most likely had a background in either military, law enforcement or some other security based profession before joininf the Westworld QA Security Force.
Arroyo assisted Charlotte Hale in the retrival of Peter Abernathy during the Attack at Forlorn Hope. He and another member of QA, Benson, entered the Fort, stunned Abernathy and managed escort him out of the fort. They didn't seem to notice Bernard Lowe. While leaving, they were spotted by Dolores Abernathy and Teddy Flood, who chased them. Arroyo and two other QA members were shot down by Dolores, Hale and Benson managed to flee the scene with Abernathy.