The reason, Sugar stocks are falling is that "The supply of sugar stock" is more than demand.
Sugar companies are having tons of sugar to be sold by august 2008. As there is more sugar to be sold, the prices of sugar will come down and reduce the profit margin for the companies. that's why the "Big players" are selling.
Average means to "reduce the price by buying more at cheaper price"
1. You have bought 1000@237
2. suppose it falls down to 155
3. if you buy 1000 more at 155 then
4. 237000+155000 / 2000 = 197
you'll be having 2000 shares at 197 rupees, and you can sell it around 240+ in 3-6 months.