After just three spring practices, the writing was probably on the wall for Petty. The depth in UW's backfield is growing and reps are getting hard to come by.
Petty was one of UW's big backs, and that position in particular is going to get more crowded as time goes on. With Lavon Coleman coming in, Ryan McDaniel coming off of his knee injury and Psalm Wooching coming off of his redshirt, there simply isn't enough room for many more carries as a big back. Combine that with the more spread out and shotgun running (read: less fullback) we may see from Steve Sarkisian's offense in 2013 and it makes sense that there would be some attrition at this position.
Petty amassed 99 yards on 29 carries in 6 games during his Husky career.