Deficit of BA unrestricted stock for the batch

Hi all,

When i key in a material for which the total stock for the storage location is 50.For the particular batch the stock is just one.But when i perform a material consumption and the total quantity which i key in is 8.But system gives an error saying deficit of BA unrestricted use-3 pcs.My concern is why it is showing deficit of 3 although only 1 quantity is there in the batch.