Why are stocks put in the T group?

Stock exchanges evaluate stocks and categorize them into groups based on certain qualitative and quantitative parameters. This is done to protect the interest of the investors and prevent illegal trading practices like price manipulation. The stocks that are put into the T group are shares that have an abnormal price variation and a sudden fall in market cap. BSE puts these stocks into surveillance mode to check if there's any price manipulation or any other illegal trading practice involved. The stock is moved into the normal segment as soon as its performance improves.