He doesn’t have much playcalling experience
O’Connell only took over as the offensive play caller after Gruden was fired by the Redskins after five games last season. Under interim head coach Bill Callahan, the Redskins would become a more run-heavy offense, which jived with O’Connell’s style.
Here’s some background on O’Connell, via The Athletic.
O’Connell believes in establishing the running game and being a run-first offense. He and Callahan see eye to eye on that particular aspect. What’s different is O’Connell’s belief in using a quick game, with play-action passes and passing more on first down, to get his quarterbacks comfortable and into a rhythm.
The Redskins went 3-8 in their final 11 games with O’Connell as the play caller, with the offense not improving until after their Week 10 bye. Haskins did his best work with O’Connell at the controls, which is encouraging.