Suppose he is playing on Bitstamp one day.
Then big price changes happen on Bitstamp, and in very short time those changes propagate to other exchanges, right?
But i am sure they propagate with some delay, maybe 30 seconds, so that if you trade on a minor exchange, you have all the time to take measures before the big change propagates to the exchange you are using.
It is always good to look into negative side before trying anything which will be involving with your hard earned money.
I'm giving you two scenarios where you may get failed with your observation :
1. There are multiple major exchanges, hence you cannot be sure a tide of new trend will always be happening where you are watching. It may or may not happen where you are watching. I guess, incorporating a bot for watching a sudden change may help in this regard.
2. Some buy or sell may not sustain within an exchange also. It means, if bitcoin is pumped in bitstamp and you are buying in a some small exchange and then you are waiting for others to rush-in. But, there will be a chances in bitstamp itself prices are getting dumped. It means a sudden wave may get neutralized within an exchange also.