On June 28, 1996, about 1600 eastern daylight time, a homebuilt, Wsk Pzl-Krosno KR-03A glider, N32113, was substantially damaged during landing at Hilltown, Pennsylvania. The private pilot and passenger were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the local flight which had been airborne for less than one minute, and was conducted under 14 CFR Part 91. The pilot reported that the glider was under tow, and as it neared the departure end of the runway (about 200 feet AGL), the tow rope became slack. He extended the spoilers, nosed over for a landing, and attempted to release the tow rope. When the glider passed over wires, the pilot felt the tug of the tow rope, and knew it was still attached. After touchdown in a field, the left wing caught on brush, and the glider was spun to the left, at which time the fuselage aft of the cockpit area was bent. The tow airplane was a Cessna 305. The tow hook was installed on the tail wheel leaf spring and held in place with two bolts. A release line ran from the tow hook to the cockpit, and was used to release the tow rope from the tow airplane. Examination revealed that one of the bolts that holds the tow hook on the tail wheel leaf spring had failed, and the tow hook separated from its mounting. Tension between the release line, and tow rope actuated the tow hook to the open position, which allowed the tow rope to be released. A check of the glider after the accident found the tow rope release operative. The tow rope would separate if tension was applied; however, when the release was actuated, and no tension applied to the tow rope, it would not separate from the glider.