Bud Selig’s failures have been exceedingly high-profile and photo-worthy . He came onto the scene in what was more or less coup against then-Commissioner Fay Vincent and quickly found himself embroiled in labor strife which led to the 1994-95 strike.
Later he presided over moves which rankled the purists: interleague play. Realignment. All manner of shenanigans with the All-Star Game.
Most notable among his mistakes in the game — and they remain mistakes no matter how much he attempts to wish them away via his pleading of ignorance — is the explosion of performance-enhancing drug use during his tenure.
Source: Craig Calcaterra, NBC Sports Will Baseball Get Better After Selig's Departure? by Charles Mager