Dillane, who plays the former drug addict Nick Clark on Fear the Walking Dead, allegedly tried to breeze through the security check points at the studio and was stopped by a security guard. Fear the Walking Dead does not shoot on the lot so Dillane didn't necessarily have access to the lot, in the first place. One guard described his behavior as "erratic" according to TMZ.
The report claims that Dillane was only further frustrated when the altercation started to get more heated and ended up striking one of the guards. At that point, the guards had had enough and performed a citizen's arrest before the LAPD arrived and booked Dillane with a charge of battery.
Dillane has been with Fear the Walking Dead since it's first episode and has arguably served as its main protagonist. Prior to the AMC series, Dillane starred in Harry Potter and the Half Blood Prince, In The Heart Of The Sea, and Sense8.
Fear the Walking Dead is currently on its midseason hiatus and will return for the back half of its second season on August 21 for another eight episode run. The series has already been renewed for a third season. Dillane's Nick Clark character was last seen alive and well, though he's future with the show was left fairly ambiguously as he parted ways with the group, electing to walk among the undead.