The only reason is weak global cues all the way from Asia to Europe.
Consider this: European stocks follow US markets.Yesterday,US markets were in good gains till european indices closed then there was a sell off and US had moderate loses.This looked bad for Asia markets as they started today and they followed weak....India opened up quite good compared to other Asia indices...note that INDIA is taking leadership at this moment(this suggests strength in out markets)....in the afternoon European markets opened again. SInce they missed yesterday US correction, they have to take the beating today and they traded with over 1% losses throughout.....even then we didn't see a selloff in our INDIAN stocks..but as time passed by conditions didn't get better....trader feared about their positions and closed their positions which is why we saw a selloff.
Here you should note that predicting other market movements can help you know the trend.
As far as I am concerned, there is no problem with Indian markets in the near-term....we are in for a ride upside...this is just a dip providing an opportunity once again for investors