It was a revolving door at quarterback for Stanford in the first half after an injury to Keller Chryst on the first play of the host Cardinal’s second series against UCLA on Saturday night. There were four quarterback changes in the first half before K.J. Costello took over and led the Cardinal to a 23-13 halftime lead. Ryan Burns was ineffective in two series before Costello got the ball rolling. There’s no telling how long Chryst will be out, but Costello looked just fine.