The word duffer was once used to describe a counterfeit coin.
Its use evolved to include a worthless person, who, like the counterfeit coin, was only taking up space, such as a duffer on a golf course.
Because they are inferior, duffers need a handicap, or help, which is really a penalty against the superior players.
The word handicap came from drawing of lots for positions in a horse race, which literally required putting a hand in a cap.
A “duffer” often needs a “handicap” because they suck at golf.