Officer Down - S1-E4
Factual error: Danny and Jackie Curatola are with ESU to make an arrest at a garage. They are behind cover with their weapons drawn. Although there is no suspect shooting at them, both Danny and Jackie have their fingers on the trigger, which is against police training unless you are going to engage a subject by shooting your weapon. The ESU officer right next to them does not have his finger on the trigger. (00:38:04)
Other mistake: Danny, while driving home with his family, hits a man with his car. Danny gets out of the car to attend to the man, but his wife, Linda, who is a nurse, does not get out of the car to render aid to the man. (00:02:18)
Continuity mistake: After the accident, Baez has a scar on her left cheek. However, during the raid, the scar moves to her right cheek and back to her left cheek. (00:27:12 - 00:49:32)
Answer: It's a common cop show plot device. If the police on the show always acted in the most logical way (i.e. not alerting a suspect to their presence) the show wouldn't have the opportunity for an exciting foot chase.