In the defensive battle south of Pskov, on 31.03.1944, the Soviets captured the town of Krapiwinka and from there threatened the road Pskov-Ostrow. In response Hauptmann Zeller repositioned his forces to shield his south flank and launched a counterattack with his reserve company and 6 assault guns from Sturmgeschütz-Brigade 184, and was able to retake Krapiwinka. Two further breakthroughs at Stremutka and Letowo were also defeated that day, with the result that the main defensive line of the regiment could be held.
Over the course of a 7 day period the next April Zeller was involved in defeating a total of 55 Soviet attacks, leading 10 counterattacks in the process. His contributions were a key factor in the German resistance and the consequent holding of the frontline. For these defensive successes he was awarded the Oakleaves to his Knight's Cross.