What is Calling It?
1.
Medical Staff term to state that an individual has passed away. Background not known (by me anyway).
"I'm callin' it, its 1900."
"Alright, get the stiff i-deed, and tagged."
See
2.
Claiming rights to something. Like calling the last beer in the fridge, or the front seat in a car. Calling shotgun.
There's one beer left in the fridge, I'm calling it!
Yo mofo! Why you drinkin' that beer? I called it!
See