They both were used, not just in injury situations, but injuries certainly muddied the situation. Fran would run option against a team he thought susceptible (Watts' 162 rushing yards against SoCar) and would sling it around as indicated by both QB's career stats. They are linked in their careers, but I think they only overlapped two years. I used them as an example because they were thrown out as two QB's who didn't work. They both represented the University well, and Zow was the career passing leader before being supplanted in the Saban era. BTW, Fran's offense was "multiple" and, although I know it's not palatable for many, Saban's offenses have been similar in some respects.
Well, a lot of what I'm going off of is a damn 20 year old memory and also from Zow's book. I know he said that Fran kind of fucked with both of their heads all through the spring in 2001 and into the fall. He told them there wouldn't be a 2-QB rotation and one would win, one would backup. I honestly need to read it again because I cant much remember how he recalled his senior year other than Fran still messed with their heads and told them they would both play against UCLA, but again maybe I'm wrong here but I dont remember Zow playing a single snap again with the starters until Watts got hurt late in the year.

