Let's say three players, NLHE. Ante/SB/BB = 100/1000/2000.
Player 1 (BB): 50 chips left
Player 2 (Button): 10,000 chips
Player 3 (SB) : 10,000 chips
100 chips Ante to be paid by everyone - but Player 1 can't pay, so he/she is all-in. 3 x 50 chips go into main pot and 2 x 50 chips go into a side-pot between players 2 and 3.
Now the blinds: player 3 pays the small blind, which goes into the side-pot. player 1 would have to pay the big blind, but is all-in and can't pay.
Does player 2 now still have to "call" a full big blind of 2000, although nobody actually posted that amount?