Even if you're bearish, I don't know why you would sell immediately after a run like that.
I agree, that's weird. Sometimes when there's a big buy, a bot will do an equally big sell immediately after. I don't understand that strategy.
This time the sell was relatively puny (~2600 btc sold after ~20k btc bought), and it was minutes afterward, so probably not a bot.
[12:43] <bitcoinRT> Jan04 17:39:35 | Bid: 5.29 | Ask: 5.321 | Last: 5.32098 | Volume: 108690
[12:45] <bitcoinRT> Jan04 17:41:11 | Bid: 5.33847 | Ask: 5.7 | Last: 5.69619 | Volume: 125090
[12:46] <bitcoinRT> Jan04 17:42:43 | Bid: 5.6972 | Ask: 5.7 | Last: 5.7 | Volume: 127795
[12:49] <bitcoinRT> Jan04 17:45:47 | Bid: 5.39216 | Ask: 5.39327 | Last: 5.39664 | Volume: 130249
[12:51] <bitcoinRT> Jan04 17:47:20 | Bid: 5.39077 | Ask: 5.39327 | Last: 5.23 | Volume: 130462
[12:52] <bitcoinRT> Jan04 17:48:52 | Bid: 5.35035 | Ask: 5.39327 | Last: 5.39327 | Volume: 130700
I guess it may be "operator" error. He noticed large buy up to 5.70 and wanted to sell into it. Not realizing the spread is huge ....
*Eureka*. Just realized that these are bitcoinica stop or trailing stop orders placed to sell at a higher price. Stop orders become market orders when a target price is breached, so they just get dumped onto the thin bid depth after the upward spike.
These sellers should use limit orders instead, or (if bitcoinica offered them) stop-limit orders.