Change in Trend

I have observed this general pattern many times. Stock A is moving up or down after 9.15 with high volumes. Suddenly at, say 10.00, 10.30, 11.00 or any other time, it reverses & starts moving in the opposite direction (down/up) for the rest of the day. What are the general reasons for this ? What should a day trader do in this case to reduce losses ?

just to enmesh small traders who go with trend

Do u mean that such reversal is good for large traders ?