Blue Bloods Season 9 Episode 18 revolves around the question of fitness requirements. After an out-of-shape officer can't run up the steps after a suspect and it leads to a dangerous situation, Frank must decide what to do. Sid is firmly on the side of leaving the requirements alone because he is a bigger guy and doesn't want to be discriminated against, while Garett takes the view that cops need to be fit to do their jobs.

Sid's day goes from bad to worse when he also learns that Danny is investigating a cold case that he was the original lead detective on, especially after Maria talks Danny out of dropping the case for Sid's sake.

Meanwhile, Erin is getting pressure from the DA to close a case against a woman accused of murdering her foster son, but Anthony has a hunch they don't know the whole story and insists on investigating before they go to trial -- and gets attached to another foster kid who lived with the murder victim and is now in a bad situation.

And when Officer Witten starts a women's group that plays sports after work, Jamie discourages Eddie from attending, but that leads to a major fight between them.

To find out what happens, watch Blue Bloods Season 9 Episode 18 online.