The term patzer is taken from the German verb patzen which means, quite literally, to make a mess. Patzers are quite simply mess makers.
This term is most frequently used in the chess world to describe a player of low skill, or as an insult to a player of any level.
Example of use
Player 1: Oh no, I have to face someone named Igor Stralavanskov in the next round. I'm doomed.
Player 2: I wouldn't get so stressed if I were you. He's a patzer.