Through the Looking Glass - S5-E19
Other mistake: Danny supposedly handcuffs an at-risk teenager. When the police officer takes her away to a cell, the girl isn't handcuffed. The handcuffs are just in her hands behind her back. (00:52:00)
Starring: Tom Selleck, Bridget Moynahan, Donnie Wahlberg, Len Cariou, Will Estes
Through the Looking Glass - S5-E19
Other mistake: Danny supposedly handcuffs an at-risk teenager. When the police officer takes her away to a cell, the girl isn't handcuffed. The handcuffs are just in her hands behind her back. (00:52:00)

The Uniform - S2-E11
Character mistake: While handcuffing an auxiliary officer in his apartment, there is a poster on the wall reading, "attention military personal..." Personal is misused. It should read "attention military personnel." (00:16:02)
Frank Reagan: I'm the PC. I know everything.
Trivia: Although Len Cariou plays Tom Selleck's father, he's only five years older than Selleck.
Question: Why why does Danny always yell, "hey!" When he's is a half a block from the perpetrators which gives the perpetrators 1/2 block head start running from Danny. Why doesn't he wait until he's close to him and he wouldn't have to chase him so far?
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.