A police officer has been kicked in the face and three others have also been assaulted during a covert operation against train fare evaders in Sydney's southwest.
The Police Transport Command officers were in plain clothes during the operation in Bankstown on Wednesday when they identified themselves and attempted to stop a man for not paying his fare.
Police said the man threw a punch at an officer and two of his friends joined in, with one officer allegedly kicked in the face by one of the men.
The officers gained control of the situation and arrested three men.
Four officers suffered injuries including a bloodied nose, a swollen elbow, sprained ankle, grazes and bruising.
Two men, both aged 19, and another aged 21 have been charged with assaulting police and resisting arrest.
Two of the men were refused bail and will appear at Bankstown Local Court on Thursday.
One of the 19-year-olds was granted bail.