Ariad Pharmaceuticals Inc fka ARIA

[glass_half_full]

It could have been that someone left a good-till-canceled stop order up over the weekend for 1500 shares.

On Monday morning, there were no bids between the last trade and that order, or a market maker realized that his bids were the only ones and simply pulled them.

Then they crossed a 500-share trade at 2.29, triggered the stop-loss order, and bought the 1500 at 2.29. Easy money.

That assumes that they actually crossed another trade at the stop price. I know of at least one video of someone's Bloomberg screen where he shows his stop order get filled and it's the only trade at that price.