A security guard at Campsfield House immigration detention centre smashed a phone with his baton after seeing detainees using it during the alleged riot, a court heard.
Group 4 guard Terry Morley told Oxford Crown Court he and a colleague broke the phone "for the detainees' own safety".
But defence barrister David Bright told him: "You used a piece of gratuitous violence to make the scene look worse for the people who are being prosecuted."
Eight West African men - Sunny Ozidede, 30, Edward Onabanjo Agoro, 27, Stanley Nwaidike, 22, Harrison Tubman, 19, Lucky Agbebaku, 28, Sambou Marong, 17, John Quaquah, 32, and Enahoro Esemuze, 26 - deny riot and violent disorder at the centre, in Langford Lane, Kidlington, on August 20 last year.
At their continuing trial yesterday, guards described how they got caught up in a disturbance minutes after removing two detainees from the centre for trouble- making.
Mr Morley said he and a colleague put out a fire in the ladies' day room and then saw two detainees using a phone nearby.
He told the court: "We told them to get out and for their own safety smashed the handset with a baton." Mr Morley said he later saw 'Lucky', 'Sunny' and 'Sambou' in a corridor where a group of detainees were beating on a door. He went to the aid of a colleague and got caught up in the violence, the court heard.
Mr Morley said: "I managed to reach him and when I got down there I was surrounded by detainees.
"They were threatening us and saying, 'Why did you do what you did this morning?' They were getting more and more irritated."
Another guard, Desmond Wilkinson, said about 30-40 detainees came "charging through a door".
He said: "A detainee wearing a bandana looked at me and said, 'We are going to kill you'. I felt extremely frightened."
The guards managed to escape through a door helped by colleagues, the court was told.
A female guard, Karen Mitchell-Hall, told the court she was confronted by a detainee - named as Sunny Ozidede - as she fled down another corridor.
Mrs Mitchell-Hall said: 'He placed his hands on my shoulders and said, 'Where are you going white bitch?' I pushed my knees up to his groin, although I do not know if I made contact. He let go."
Guards later gathered in riot gear to secure a gate to the detention block which was forced open by the weight of 80-100 detainees, the court heard. They also saw smoke billowing from the library.
The case continues.
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