At 18:30 CDT, a Pitts S-1-11B biplane was substantially damaged following a loss of control while executing a precautionary landing following an engine/propeller overspeed near Katy. The pilot was not injured. The pilot said he had been operating in the aerobatic box above the airport for about 15 minutes. He had performed a hammerhead stall and the propeller and engine oversped, so he elected to make a precautionary landing on runway 27. He said he touched down about mid-field and applied brakes to exit the runway but the left brake failed. The airplane ground looped and came to rest inverted. The inspector verified that the master cylinder for the left brake had failed, and braking was not possible. The 1998 airplane had accumulated a total of 160 hours since new.