can't hit the broad side of a barn
Have very poor aim. For example, That rookie can't hit the broad side of a barn, let alone strike anyone out or, as put in The New Republic (February 19, 1990): "Their missiles couldn't hit the broad side of a barn." This hyperbolic term, dating from the mid-1800s, at first denoted poor marksmanship. Around 1900 it also began to be used in baseball, for a pitcher with poor aim.