15The Designated Hitter
Yes I know this is not a popular belief but the designated hitter is not at all what the game of baseball was meant to be for. The nine players that take the field should be able to come up to the plate and bat. The reason why this is number 15 is because I can understand and appreciate the art of a David Ortiz or Edgar Martinez. It is not a terrible rule that was put in place in 1973, but the fact that one league does it and the other does not, hurts the rule.
We've seen the conflicts of this rule on full display in the World Series year after year, as the DH exists in American League ballparks, then switch back to tradition once the series shifts to the National League team's ballpark. With Ortiz set to retire, perhaps the DH rule should be retired as well.