Take Ftse future for example. Say it's 4502 trading, so nearing a crucial level (4500). A big player might see the volume go thin on the buy side and put a sell order in down to 4495 to flush out the stop orders below 4500. It briefly trades down to 4495 which is the low tick. There is no other selling about other than stops around 4500, and the market directly recovers above 4500. The "low ticker" would have had buying in place beneath 4500 to pick up all the cheap, weak longs that are stopped out.