Well, I would think most activity would be pre-market after an earnings report (I'm guessing these are always done after market close and never during trading hours?).
I guess what I'm saying is, the underlying may see a lot of volatility due to bears bringing the price down in order to buy the dip and sell the top if report is positive.
I don't really know. Fortunately, I've never had to react to a bad earnings trade in after hours or pre-market by trying to exit or adjust a position. It would seem to me that since most large institutions hedge with options, they would not be able to do much in the pre-market until the options start trading. Due to the lack of liquidity in after hours, it seems to me that they would only trade if they are experiencing an "oh sh*t!" moment and are forced to adjust a position.