Mantler is on trial for assault causing bodily harm for kicking Buddy Tavares during an arrest in Kelowna in January 2011.
The incident was caught on video and went viral shortly after it was posted online.
Const. Kyle Boffy told the court Wednesday that officers are trained to wait for back up when they pull over a suspect they believe may be armed.
The video shows Mantler approaching Tavares with his gun drawn before other officers had arrived.
Under cross-examination, Boffy agreed police radio dispatches portrayed Tavares as a dangerous suspect with a gun. Boffy said there was a perception of a real threat to public safety.
The officer was also shown the video frame by frame leading up to the kick Mantler inflicted on Tavares.
Tavares is on his knees, moving his hands towards the ground, but for three frames, his hands move upwards.
Boffy agreed with the defence lawyer that the change in movement could be seen as threat, and possibly signal Tavares was going for a weapon.
Tavares' sister Pam Weiher said later outside the court that she sees it differently.
"I think they are kind of grasping at straws. Three frames is miniscule. It wouldn't even be visible to the naked eye, or in real life," Weiher said.
Three frames of video represents a time span of about three-tenths to one-eighth of a second.
Under Crown questioning earlier, Boffy told the court he would not have approached Tavares in his truck as Mantler did, as it did not accord with RCMP protocol for an officer confronting a potentially dangerous person on his own.