Calculating the Probability of Sustained Loss

[Lebronomania]

Could anyone tell me how to calculate the probability of a winning player sustaining a certain loss or greater over a certain period? Here's the example I wanna work out:

Player wins 1.5 BBs an hour. His standard deviation is 12.7 BBs an hour. What is the probability that he will be down 120 BBs or more after 106 hours? What if he wins only 1.0 BBs an hour?