Mickey Slaughter (1963-66)
For the first two entries on this list, I have them lower due to the AFL being brand new, the Broncos being a brand new franchise, among other things. First on this list is a quarterback who would start 19 games for the Denver Broncos during his four-year career.
Mickey Slaughter did not spend a whole lot of time in the league, but he took what was given to him in his time with the Denver Broncos. The results were 22 touchdowns and 38 interceptions.
Granted the Broncos were a new team, it is expected to have these results. But after Frank Tripucka, Denver struggled to find a solid starter.
In no way is Slaughter the worst quarterback on this list. There will be others that were way worse. The quarterback just was playing on a team that was still very young and there was not a lot of talent surrounding them.